I can understand how difficult this must be for you - I'm sorry you're afraid of how your mom will react to your pregnancy. There aren't really any easy answers here, but I will be praying that everything will work out for you.
Focus on the Family has some information for pregnant teens on their site - here's the link: http://www.focusonthefamily.com/pregnant.aspx?p=1157699
I work with Focus, and there are counselors available to speak with you over the phone if you think that would help (it's free). http://family.custhelp.com/app/answers/detail/a_id/12?p=1157699
God bless you and your baby!