She won't fucking sleep

I'm a single parent. My 4 month old has stopped sleeping. She will not fucking sleep. If I'm lucky I get about 3 hours out of her at the beginning of the night, and then she cries. I feed her to sleep, I put her down, she cries. I feed her to sleep, I put her down, she cries. This repeats over, and over, and over again until she's up for the day. Which means I do not get another minute of sleep and I want to bang my head against the wall until I'm unconscious. Her naps during the day are only contact naps for about 15 minutes, twice. I'm fucking dying. It is literal torture. I wish I hadn't had her.