I feel like a piece of shit mom..

My son is almost 16 months and he still isn't able to self sooth or put himself to sleep. He's relied on all kinds of different ways for us to help him...and I'm trying to put a stop to it. However my fiance and his parents seem to be able to put him to sleep and naps by holding him and playing music ( Bob Seger mostly ) until either he falls asleep or is dozing and they place in the crib. For me he refuses to do that. He kicks and screams and now hits. I've tried cry it out and I get so sick over hearing him scream....but I also think I suffer from ppd . I never got help because I couldn't afford it and I think it's gotten so much worse...I get short with everyone and cry. But more to the point, I have been trying all day from 10:30 am to now to get him to nap. We almost had it this morning but by almost noon he lost it and my back couldn't handle holding him anymore. I gave up , I made him lunch and about a half hour later I tried again. He won't stop screaming...and doing everything I mentioned above. I started to cry and I put him in the crib and walked away. I really started to cry when the moment he saw me leave the room he started screaming frantically like I was abandoning him. I went into my room and screamed into my pillow because I feel like I made a mistake becoming a mom. I love my son more than anything but never has it been this hard for us to do naps or sleep....and I am really feeling like a garbage parent. Like i should have never made this decision. I hate myself for even feeling this. I don't know if I really feel regret...but I know I feel like a piece of shit and a terrible mother and I hate that he's going to have me as a mother for the rest of his life. I don't know what to do...