Hey FJ

It sounds like you're really trying and doing a great job, so don't doubt yourself.
I'm not a parent (yet) however to me, it sounds like perhaps he's just wanting attention unnecessarily... perhaps the new baby on the way is creating some anxiety for him? He feels perhaps once again he'll be replaced by another baby? Sometimes older siblings have these feelings anyway i've heard.... my sister (she is the eldest) was the most trouble for Mum and Dad aswell. Mum thinks its cos she wanted all the attention on her and when me and my younger sister came into the picture she found it harder kwim??
May not be that but just a suggestion.

Can you and Evan spend some quality time together just the two of you? Go to a park near you and just play on the swings etc together without the distraction of the other kids around? Would that help? Allocate 'Mum & Evan' time once a week even just for 1hr. When DH gets home from work so he can look after the kids?

Hope he calms down soon for you....maybe seeing the teacher might help.... good luck hun.