Tell your mom as soon as possible, it's scary, but it feels great to get rid of that stress & have it "out in the open".. I waited until I was 10 weeks to tell my parents.
I told my mom one night when we were home alone together.. things were rough with me and my dad for a bit, but my mom has been fantastic all along & everything is going well for us, they're helping me soo much! Even if they weren't going to help me out, I think it's better to know what sort of support you can expect so that you can get on with planning/saving/buying/appointments etc.