Hi Chickz, oh I really feel for you, I do! My DD was very similar and the first year was awful, second year a bit better, and then better by increments ever since. I know it's no bloody use to you at the moment but it WILL get better! No magic solutions, I doubt she'll change overnight, but for my DD at least things did markedly improve once she could talk. Like others have said, I think she - and probably your DD - are/were just very frustrated by babyhood and not being able to communicate and do/get what they want on their own.
My DD is nearly 6 now and TBH she is still a handful sometimes - very sensitive, very headstrong, can have awful tantrums. BUT - things are so much easier when you can have a conversation with them, honestly they are. She is also very smart, funny, very confident and independent, and so so kind and loving.
I wish I could help more because I know it's no good when people say, Oh, they'll grow out of it. You need help HERE and NOW. All I can say is - be kind to yourself, find any way you can to do things for yourself here and there. Do you have a partner who can take the strain sometimes? Like you, I found going back to work part-time really helped, but also going out in the evenings, seeing friends on your own, going for a massage (if you like that kind of thing), buying little treats - maybe it sounds trivial but I found that if I gave myself little "rewards" then it made the stress, anxiety, etc a bit better.
Do you have friends you can rant at, who won't judge but will just prop you up? I know you say other babies you know are calm, but do you have friends with older children, or indeed friends without children who can listen? Counselling services via your GP? I know you're on anti-depressants, but you could take the two-pronged approach... Anyway, just to say I really sympathise and I'm sorry you have it so tough. Feel free to PM me if you like, if you want to chat...