I have three kids, not quite so young (7, 4, 2). I nearly left whilst pregnant, but didn't until my youngest had just turned one!
I hope that you are getting alot of support from your midwife, there are specialist midwifes to help stressed out mums to be!
Also, sure start will be a great source of support with your toddlers!!
I'm sure that you will find lots of help and support on here, and will make some good friends. I've only been on here about 4months, but feel so much better for it!
It certainly fills the nights in a little!
Good luck with your pregnancy.