Sorry you're having such a rough time.
It's obvious you're doing a great job, holding things together, that you're a tough cookie keeping on, and your family are very lucky to have you.
Sorry, I can't see if it's the rough time, or the depression that's really getting you. If it's depression, please talk to your GP - antenatal depression does happen. The health services are great if you need them - the health visitor came every week for months to check up on me and was a great safety net. But please talk to the GP now, as if it's antenatal depression they should know asap. (Mine wasn't recognised and spiralled out of control)
Have you tried the citizens advice bureau? Good source of advice on possible benefits, etc.
There are some great comments about exercise, healthy diet, sunshine, plus I find comedy and music are great too. And please get plenty of sleep.
Sorry, gotta crash.