Your son and mine could be the same. When I was in the lead up to having a baby my son was 18 months and he turned into an absolute feral. We tried everything to sort it out.

Unfortunately, it seems that only time and growing up has really helped. My LO is now 9 months and he is nearly 2.5 and he's much, much better.

I agree with the others. Clear out his room and see if that helps.

For your own sanity, focus on the areas that you are having the success with. With the baby coming, you really need to keep a good headspace. I know it's hard though.