I want my son's father to sign over his right's (we haven not been together since I was 3 months pregnant, he was not there at the birth, but he he says he needs time to think about it)... it's been 4 months. What should be my next step, legally to get the ball rolling?

There is nothing you can do legally to make him sign over his rights except maybe prove that he is unfit or abusive. It is a hard decision he's making, that will make a difference in his son's life. He may not be that active now, but depending on his age and maturity level that can change. He will be giving up every single bit of say in his child's life if he does this and even if he is a lousy dad, his son is still his blood. Its tough. Have some patience.

Why haven't you filed for child support? Why would you want him to relinquish rights?

As alkaline said, you cannot force him to relinquish unless you can prove he's a danger to the child.