I think it would be in your best interest if you went ahead and got a test. This way if you are, you can be more aware of you and your baby's health needs. Also, if it turns out you aren't, then you won't have to worry about telling your mom.
Second, you are afraid your mom will think badly of you. She may be mad at first, but after time, she will realize that this is part of life. It more than likely will be hard for her at first, so be considerate of that.
Last, if it turns out you aren't pregnant, then the best thing you should probably do is get on the pill. This way, you won't be ashamed to have to tell your mom of an unexpected pregnancy, since you said you are scared of what she will think of you.
Just hang in there, and I hope you get the answer you want! But, go get a test asap!!!