No. Conservation of mass and energy only prohibit the total mount of mass and energy changing. The universe could have always existed with that mass and energy. We have good evidence that a lot of mass and energy was spread out by the expansion of a much smaller universe around 13.8 billion years ago, but we don't know what the universe was like before that, it could have always existed, or it could have been formed by the collapse of another universe, we don't know for sure.

Anyway, the laws of physics are just empirical observations, they have been proven wrong before. Einstein's general relativity disagrees with Newton's laws of motion and, further study reveled that Newton was (very subtly under normal conditions) wrong.

Wrong, it was GodGod

The problem with this reasoning is that it assumes 'nothingness' as a default state, despite the fact that nothingness seems to be a philosophical concept incapable of actually existing (even in a vacuum there's zero point energy).

So "how did we get something from nothing" necessitates the task of proving a plausible case for nothingness as an initial state.

And the answer of 'God' as a mechanism just kicks the can up the road, as then you are faced with the question of what created God.

If you claim eternal preexistence of God, then you've landed at the same rejection of nothingness as an initial state just with unnecessary extra steps.