Consistancy and boundaries. Whilst I know you might not have the energy but maybe establish a "thinking spot" for quiet time when he isn't listening. We have the thinking chair and the thinking step in our house and it sure does stop me from blowing my lid (yes sometimes I'm not perfect) but it gives them time out and me time out so I can calm down LOL! I know it sounds harsh but you need to try and establish some boundaries now, because its even harder when bubs is here. Paris was 3 when I was pg with Seth (nearly 4) and we went through similar power struggles. I just made sure I took more time to communicate, follow through with promises (be it promises of attention or consequences of actions) and try to have some quiet activity time together daily, where you can sit down and do something together. Even if its puzzles, or watching their favourite show in bed. I used to nap a lot during pregnancy so when I would have a nap we'd lie in bed and have "chatters" and talk about all sorts of things, some days we'd just talk about fantasies (when I grow up my house will be...) or even just eye spy. But then you are getting the rest and they are getting the quality time.

Goodluck Its hard I know but there is light at the end of the tunnel.