Well, all I can say is that you should really take it easy and don't stress out. You do need to tell your mother and try to look at it as something positive. You have a child with a beating heart growing inside of you and you should be happy about that.
My cousin was pregnant at 14 a few years back and she talked it out with her mother. Her and her mother were never really that close until the baby came. Then my aunt realized that she needed to spend more time with my cousin and supported her 100% my cousin graduated from high school with 3.9 gpa and went on to college and did everything that she wanted to do. It wasn't easy, but she realized that it was time to take everything serious for the sake of her baby.
Some people might view your situation and tell you to consider adoption and so on.
I suggest that you listen to your heart and do what you know is right.Hopefully your mother supports you and helps you out with this. It will really make things much more simple once you know that you have the support of your mother.