No it doesn't. The first Law of Thermodynamics states that the amount of energy in a closed system will not change, i.e. ENERGY cannot be created nor destroyed. Energy makes up matter but can exist in its own right. So the amount of matter now is not necessarily the amount there was a second ago or a thousand years ago.

The composite substance matter/energy cannot be created or destroyed. But matter can be converted to energy and vice versa. The sun converts about 1 million tons of matter to energy every second.

That is true. An atom of oxygen you breathe in has been there since the beginning of the universe. Energy and matter con be converted but cannot be destroyed or created.

Principally, yes. However, "we can only speculate on the extent of the universe, making it impossible for us to give a definitive answer for the mass of the universe". 1) "The term mass in special relativity usually refers to the rest mass of the object, which is the Newtonian mass as measured by an observer moving along with the object. The invariant mass is another name for the rest mass, but it is usually reserved for systems which consist of widely separated particles. The invariant mass of systems cannot be destroyed, and is thus conserved so long as the system is closed. The term relativistic mass is also used, and this is the total quantity of energy in a body (divided by c2). The relativistic mass includes a contribution from the kinetic energy of the body, and is bigger the faster the body moves, so unlike the invariant mass, the relativistic mass depends on the observer's frame of reference. Because the relativistic mass is proportional to the energy, it has gradually fallen into disuse in among physicists. There is disagreement over whether the concept remains pedagogically useful." Source and further information: http://en.wikipedia.org/wiki/Mass_in_special_relativity 2) "In special relativity, the conservation of mass does not apply if the system is open and energy escapes. However, it does continue to apply to closed systems. In relatitivy the conservation of all types of mass-energy implies the viewpoint of a single observer (or in the view from a single inertial frame) since changing inertial frames may result in a change of the total energy (relativistic energy) for systems. However, for the special type of mass called invariant mass, changing the inertial frame of observation for the whole system has no effect on the measure of invariant mass, which remains conservered even for different observers who view the entire system. The conservation of mass may be cast in terms of the conservation of a system combination of energy and momentum, which is conserved, and which gives the same invariant mass of any system (such as the two-photon system) for any observer. In another example, the conservation of mass also applies to particles created by pair production, where energy for new particles may come from kinetic energy of other particles, or from a photon as part of a system. Again, the invariant mass of closed systems does not change when new particles are created. However, the principle that the mass of a system of particles is equal to the sum of their rest masses, even though true in classical physics, is false in special relativity. The reason that rest masses cannot be simply added is that this does not take into account other forms of energy, such as kinetic and potential energy, and massless particles such as photons, all of which affect the mass of systems. The mass-energy equivalence formula implies that bound systems have a mass less than the sum of their parts, if the binding energy has been allowed to escape the system after the system has been found by converting potential energy into some other kind of active energy, such as kinetic energy of photons. The difference, called a mass defect, is a measure of the binding energy in bound systems — in other words, the energy needed to break the system apart. The greater the mass defect, the larger the binding energy. The binding energy (which itself has mass) must be released (as light or heat) when the parts combine to form the bound system, and this is the reason the mass of the bound system decreases when the energy leaves the system. The total mass is conserved when the mass of the binding energy that has escaped is taken into account." Source and further information: http://en.wikipedia.org/wiki/Conservation_of_mass 3) "In special relativity, the invariant mass (hereafter simply "mass") of an isolated system, can be defined in terms of the energy and momentum of the system by the relativistic energy-momentum equation: m = [sqrt(E²-(pc)²)]/c² Where E is the total energy of the system, p is the total momentum of the system and c is the speed of light. Concisely, the mass of a system in special relativity is the norm of its energy-momentum four vector." "Generalizing this definition to general relativity, however, is problematic; in fact, it turns out to be impossible to find a general definition for a system's total mass (or energy). The main reason for this is that "gravitational field energy" is not a part of the energy-momentum tensor; instead, what might be identified as the contribution of the gravitational field to a total energy is part of the Einstein tensor on the other side of Einstein's equation (and, as such, a consequence of these equations' non-linearity). While in certain situation it is possible to rewrite the equations so that part of the "gravitational energy" now stands alongside the other source terms in the form of the Stress-energy-momentum pseudotensor, this separation is not true for all observers, and there is no general (in other words, covariant) definition for obtaining it." 4) "What is the mass of the universe? What is the mass of the observable universe? Does a closed universe have a mass? None of the above questions have answers. We know the density of the universe (at least in our local area), but we can only speculate on the extent of the universe, making it impossible for us to give a definitive answer for the mass of the universe. We cannot answer the second question, either. Since the observable universe isn't asymptotically flat, nor is it stationary, and since it may not be an isolated system, none of our definitions of mass in General Relativity apply, and there is no way to calculate the mass of the observable universe. The answer to the third question is also no : the following quote from (Misner, et al, pg 457) explains why: "There is no such thing as the energy (or angular momentum, or charge) of a closed universe, according to general relativity, and this for a simple reason. To weigh something one needs a platform on which to stand to do the weighing ... "To determine the electric charge of a body, one surrounds it by a large sphere, evaluates the electric field normal to the surface at each point on this sphere, integrates over the sphere, and applies the theorem of Gauss. But within any closed model universe with the topology of a 3-sphere, a Gaussian 2-sphere that is expanded widely enough from one point finds itself collapsing to nothingness at the antipodal point. Also collapsed to nothingness is the attempt to acquire useful information about the "charge of the universe": the charge is trivially zero."" Source and further information: http://en.wikipedia.org/wiki/Mass_in_general_relativity