I feel like I should have never gotten pregnant

I'm suffering from ppd/ppa. My lo screams all the time but is healthy. I feel like the worst mother in the world and that I should have never had her. I love her, but I'm so miserable.
She can't sleep by herself at all. I have to nurse her to sleep for every nap and I have to go to bed when she does. She's 4 months old, we can't sleep train because a) she's too young and b) she gets hysterical and won't settle down - tension increaser. She also has numerous food sensitivities - milk, soy, peanuts...and I can't have caffeine or alcohol (no I'm not going to pump and dump).
I'm medicated on Zoloft, and I'm in therapy. I think my husband is depressed too - we can't find any time to be intimate and he hates that he can't help me.
I don't know why I'm really posting this. I feel terrible, but I feel worse for even thinking that I ruined our lives by wanting this little girl so badly. My sil had a baby at the same time and hers is perfect - sleeps and barely cries. My DH's family expects us to be able to parade lo around the same way and we just can't. I'm so exhausted and she's only 4 months!
Please someone, anyone tell me this gets better?
I don't even feel like I exist anymore, and I feel selfish for wanting time to myself.
Sorry this is so all over the place.