And by the way, don't be worried. These bumps don't sound serious and may not even be abnormal. But one way or the other, get professionally checked, with or without your mom's help.
Your school nurse also can probably help. In most if not all schools, the nurses don't have to tell parents when kids seek confidential advice.
If your mom knows about the sexual abuse or rape you suffered when you were young, and if you haven't been sexually active since then, for sure you can speak with her about this. But if you feel you can't -- for example, if you have been sexually active and don't want her to know -- you can get care without your parents' permission (if you're in the US). In all states, laws permit diagnosis and treatment of minors for possible STDs without parents' knowledge or permission -- and often for free, e.g. at a health department STD clinic or family planning clinic. Call your local or state health department (or search online) to find out the options in your area.
But probably all you'll have to do is tell her you're not feeling well and see the doctor. Any doctor will be able to examine you and you and the doctor and you can decide what to do next.
Don't worry about talking to your mother. I'm sure when she was 15, she was "exploring" too, even if you have to say something.
Be well.
you are your mothers daughter she will love you even if you make a mistake .parents may be dissapointed with our choices at times but now that i have become one i think your health will be that much more important to her that she will be happy you came to her with your problem .i am sincerley sorry to hear about what happened to you when you were younger.is your mother aware of this?if you arent ready to discuss this with your mother yet you can still tell her you need to see a gynecoligist.without divulging all.but at some point this may be something you might want to share with her. it may bring you closer together.it could be helpful as well to have her input and knowledge .to make sure you recieve thorough treatment .good luck i wish you well