What can I legally do to get child support from my child's father?

My ex boyfriend who is the father of my child has custodial rights of my daughter, she lives with him but I'm still the legal parent. He took me for child support almost over a year and a half but my living circumstances and job changes is making it difficult to pay, he paid me support when she lived with me, but I quit asking for support because he was always threatening and his family harassed me. When I got a new boyfriend about a year after we broke up he fought all the time about support then lost his job so I was being nice and decided not to ask him for support, legally done at domestic relations. When the new boyfriend moved in my ex harassed me all the time about his daughter living under the same roof, my life was hell, from the ex and his family. I let my daughter move in with him starting in 2011. Then he had papers drawn at an attorney office to have her legally at his address as the custodial parent but he still has to consult me on school, travel, medical etc. He also put in the paper he would not seek child support. He did about 5 months later, but at the first hearing he threatened me and said if I relinquish my parental rights to him he will stop the child support, I refused then. Now after all this time, I have been paying the support from an old job and I make less at my new job. I have ask him to stop support or give me a break for a few months until I get my life together, he refuses to do so. I have begged him and even said I will relinquish my rights as her parent because I cannot pay. I even talked to domestic relations about a new hearing to modify the payment and they said I could end up paying more because I wasn't paying the full amount only an agreed amount. I am a college student working a part time minimum wage job. I have tried talking to him because I can’t pay my bills or child support and I'm scared I’m going to go to jail. He is playing a game, he said he is not working and hasn't worked for nearly the whole time.