Marriage Under 18

I am seventeen and pregnant. I am no longer living with my mom, but living with my older sister. I want to get married to my boyfriend who just turned eighteen, but my mom said she will never sign the marriage license. I won`t be eighteen until four months after my baby is born, but I want him to be living with me when our baby is born. The other problem is that his mother is opposed to us living together before marriage. So the only way for us to be a family before our baby is born is to get married. What are my options?