I'm also going through the same thing. My ex-girlfriend and I are having a child in a couple months, she wants the child to have her last name, and isn't giving me any say in the first name even.. I was wondering the legallity of this and what I can do

First its not a good idea to piggyback your question on someone else's. This can lead to confusion. You should start a new thread. So I've moved your question to its own thread.

I would consult a Family Law attorney in your area. Depending on local laws, you MAY be able to file a pre-birth injunction to prevent the filing of the birth certificate pending establishment of paternity and custody issues.

Once the child is born you immediately file for custody which will also involve a paternity test. Once this is established, you may then have to deal with a mediator to agree on naming.

Let me temper ScottGem's posting by stating that MOST states leave the decision 100% up to the mother and even a court will not stop her from naming the child whatever she wants.