Energy and the rules about creation of new energy are contained with the Universe. We have no clue how this would function outside of the Universe. Maybe there's an infinite supply of energy there - more than enough to spawn billions of Universes. Maybe the normal rules of physics don't apply (quite likely, actually) and creating a Universe winds up kicking off a process that spawns two more Universes. I'm not sure how testable any of this is - that's a question for physicists - but you certainly can't discount a multiverse because it would use up all the energy in the Universe.