You've got a lot happening in your life at the moment so don't be hard on yourself. I've suffered with depression a lot in the past and have had a few days of it throughout this pregnancy too. I'm also 31 weeks (well in a day or two) and feel overwhelmed at times.
I can't offer huge advice, sometimes that isn't what you want anyway is it hun, you just want to thrash it out, have a cry and get it out.
I have conflicting thoughts on what to suggest as my natural instinct when I feel like you are is to close the curtains, put something on the tv, eat something nice and basically comfort myself in pj's etc. BUT my counsellor says that at these times don't let it get out of hand, ok have some time to rest and recoup but then get yourself dressed, get outside for a walk maybe, do ten mins tidying or cooking. Basically 'Action inspires Motivation' not the other way round. If you wait to feel ready that time may not come. I'm not lecturing, its a real fight to get myself going when I'm down. I still feel the occasional day of sofa comforts is absolutely fine, especially when pregnant. Just be aware of it dragging on more than a few days. I know I can easily not go out the house for a week if I'm in that sort of frame of mine. It doesn't help me in the long term.
If it makes you feel better its 3pm and I'm in pj's, not even brushed my teeth yet and all I want to do is lay here eating and watchin tv. The longer I've left it the less I want to move. It's not great, but I'm aware of it and I will get myself in the shower in half an hour then get dressed, walk to the shop, maybe tidy the kitchen while listening to some comedy (usually Ricky Gervais!) on my iphone whilst doing the kitchen and I guarantee I will feel so much better for that. Then if I want to chill again after thats what I will do.
Take care xx