DS1 is nearly 7 & DS2 5 months & I'm tearing my hair out. There's so much I could write but in brief his behaviour has massively deteriorated. He was basically a good kid, if a bit stubborn, sensitive & prone to tantrums. Now it's as if he's literally had the equivalent of a child's nervous breakdown - defiance, tantrums, lashing out, backchat - half the time I'm really angry with him & trying (often unsuccessfully) to keep my temper & the other half really worried cos he just seems like such an unhappy little boy now. I could go into so many specifics but the other thing that I think is important is that he's had very little chance to socialise outside school or nursery. We live far from both our families & I've not managed to make friends in all the time we're here so it's always just me and h
Family therapy would be my suggestion, he sounds like he's having a really tough time adjusting.
Does he get much time with his dad? How much 1-2-1 does he get with you now that the baby has arrived? This sounds like it could be more than just jealousy. You could try talking to him about how he feels (I've found emotion faces useful); maybe he feels pushed out/replaced/not as important to you now so acting out is his way of making sure he gets your attention/you notice him/you don't 'forget' him (children are not always logical...especially when they're distressed).