If I am married and pregnant and my husband is not the father but he is still trying to fight me for custody, what are my options?

Yes, you need to seek help from a Matrimonial and Family Law attorney in your area as soon as possible.  You definitely want to file an answer to the divorce so that you are not in "default."  Generally, a child born to a married couple is assumed to be the offspring of both of them.  The he would be placed on the birth certificate.  You would need to have a paternity test done when the child is born to confirm what you think you already know.  If his name is on the birth certificate  it can be removed once paternity is established (or unestablished in this case).  There may be a mechanism for delaying the filing of the birth certificate given the pending proceeding and the issues involved.  Also talk about the custody issue with the attorney should the child turn out to be his after all. Good luck.