<human>: Can you summarize the given text in a few sentences?

Throwaway for obvious reasons. I hope this is an appropriate subreddit.

I recently found out from facebook that my ex-girlfriend just had a baby girl. When I asked her about it, she told me that it was mine. 

I am more stressed than I have ever been, and have trouble sleeping and constantly feel like throwing up. I am in no way ready to be a father. She had said she was on an IUD so I had thought we were being responsible. I am also not completely sure if I am the father, as she also had something going on with someone else near the time we broke up. 

My ex says that my name is not on the birth certificate (but I can't know for sure). She never told me about it and if I didn't confront her I don't think she would have told me. At this point, she isn't asking me to help or be involved, and she seems intent on raising the baby on her own, but I know that that may change.

I don't know what to do. What action should I take? Or should I not do anything if I am ok not being involved? What are my legal rights to not be involved? Do I need a lawyer?
<bot>: Ex-gf had kid, didn't tell me it was mine until I asked, don't know what to do