What can I do to fight for custody?

Im 17 and my ex is 17 as well. We have a one year old daughter between us. She is my everything. Well today she went to stay the night with her dad, and he refused to bring her home. He is filing for full custody and keeping her there. I contacted the police, since hes the father theirs not much I can do. I live in PA, and my ex has been in and out of the psychiatric center for bipolar disorder and suicidal threats he also has MULTIPLE charges against him including Breaking and Entering, Assault, Grand Theft Auto, Harassment and Fighting. He has been sent away many times and he is currently on Probation. He is also into drugs. Or used to be. I have never had anything filed against me, and I have no criminal history. He is trying to take her because I fed her KFC, at a year old, and because she has a bruise on her face from where she fell down. However, his parents breed English Sheepdogs and one of them nipped at her once! I believe tots fall down and tots hurt themselves, so I dont think he has much of a point there. Also he said she was pulling on her ear and when he took her to the hospital she had a ear infection. Well, she wasn't doing that around me until very recently and when I noticed it I made her a apointment, However, he took her before I could take her to the hospital! The last reason is because I move around a lot, but that is because I am trying to get school figured out and find a good stable home for my baby. I live with wonderful people who treat my daughter wonderfully, because I am their neice and my daughter is their great neice.Please tell me what I can do. Im not a bad mom. I love my daughter to death.