I think PTSD after divorce, or something similar must surely be a thing. the breakdown of a relationship is major – it's somebody you loved becoming somebody you don't know (in a lot of situations) and him turning nasty over your DS must be so hard to deal with.
My DH (or Dear Fuck Face Wanker) left me and our almost one year old two months ago after I rumbled his really poor excuse for an affair with a girl who was 10 years younger than him! ARSEHOLE!
The shock of it (although I now see it wasn't that much of a shock, he'd been acting disgracefully for ages) has made me feel like somebody else. I look at our wedding pictures from 3 years ago and wonder who the hell the bride in the photos is. I feel like I've aged about twenty years. I just don't feel like me. Becoming a single mummy is a complete change of identity, so it's normal, I think to not feel like yourself for a while. You will though –and you'll be stronger for it.
That said, are you getting the right help? Do you have some time to set aside to do some stuff that will make you feel like you? Stuff you know you liked doing before things turned crap? Is it worth speaking to your GP and maybe seeing if you can be referred for counseling to help with the stress of your ex's continuing bad behavior and coming to terms with things?
I've found going for a run (I ran pre baby) gives me a real boost and even though I don't feel like it, ringing a friend just for a quick chat lifts me. Left on my own I feel like a pile of crap a lot of the time, just lost and like I don't know what to do with myself. I hope that stops eventually. Stay strong, and in the words of John Lennon, everything will be alright in the end, and if it's not alright, it's not the end.