Order some progessence plus from Young living for after baby arrives. It will help to naturally balance your hormones so you can avoid the highs and lows. Right now, there isn't much he can do for you, you are uncomfortable, tired, and probably a little out of sorts. I would recommend lavender and/or peace and calming to help you get more rest and feel more yourself. Good luck.
It's probably due to hormones and will hopefully change after birth. Sounds like he really wants to help you but neither of you know how. Sleep deprivation and weighing more that usual is uncomfortable and hard to get the SO to understand or know what to do about it. Try figuring out other stuff he can help you with so he knows he's doing something useful and you don't need to deal with that and can focus on rest and be comfortable.