How can I get the mother get me through paternity test?

I had a 3 month relationship with a girl and got her pregnant; so she claimed until she was 5 months pregnant. But she was back with her ex-boyfriend. The baby was born in November and she refuses to give me a paternity test. I know she is my baby; and I want to be part of her life. The girl's boyfriend signed the birth certificate. I want her to take a DNA test. I want her to be punished by law for forging a birth certificate, putting me through emotional hell, and robbing me of the birth and first year of her life. What can I do? I am on a limited income, but willing to fight for my child.