My Angry 3 year old

I am currently 37 weeks pregnant and I have a 3 1/2 yr old son. My son has been great during my whole pregnancy but as of last week he's turned into a little terror whenever my husband leaves the room...
He has balled his fist up at me, attempted to run and then jump and land on my belly, he has been talking back, snatching things from me...
I do not know what has happened to my sweet little boy but all of his aggression has been towards me. I'm doing everything exactly the same. The oddest part of the whole thing, is that he'll do something wrong and then get sent to time out and just cry "Mooommmmyyy....I wannnt my Mommmmmyyy" Right after he just got done trying to hit me!!
Any thoughts??

He is probably just sensing that things are about to change. Maybe you are under a little more stress trying to finalize things for the baby and he realizes that you wont have quite as much time for him once baby gets there. Try to make a point of spending alone time with him, read a book, have him tell you a story. I dont know about the hitting and all how to stop it cause my kids have never done that but he is at the age where agression is going to come out more.

jealous of the baby. Teach him a good big brother doesnt hit.

the nephew did the same thing about two months b-4 his mom gave birth he is three today, the baby is six week now and he still does it! i think it is jelousey and a cry for attention, but it needs to be nipped in the butt now b/c he has become a little terror. mabey some videos that help him get used to the idea of a new baby?!?

Maybe he is just really scared? I know he is young but have you sat him down and told him he still going to be your #1 little man, and he is going to have a baby Brother? (just guessing new baby's gender?) I've heardin pshyc, some children they feel like they aren't good enough anymore and thats why mommy needs a new baby... Just let him know he is going to be a big part in this new babys life!
IDK, maybe thats helps?

Thanks for all the feedback...I have been very exhausted. I probably do need to spend more QT with him. We talk about the baby, he asks me questions about her, he likes to go into her room and check everything out. He probably can sense that she'll be here soon.