It's likely to be a blocked pore or ingrown hair, which can get a little pus and get infected, swell and hurt. Try what's called a "sitzbath," basically a term for sitting in some water in the tub that you don't bother to fill as high as a normal bath. Just put some water in, and sit in it, and soak. You can also put some white vinegar in the water if you have it, or some Epsom salts. The warm water should cause the blocked pore to open and drain. If you have Neosporin or Polysporin, put some on the spot after your bath. Also, wash all your underwear in hot water, so there is no chance of them adding any bacteria to the mix. This is a pretty common problem so if you do tell your mom, you'll probably find she takes the news pretty well. :)
ps -- You can also make a hot compress with a (brand-clean), wet washcloth and put it on the area a while. If the inflamed spot does not open and drain after a few treatments of heat and moisture, there is the possibility it's a cyst. If it continues to hurt or gets bigger, and you can't get it to drain, see your doc.
I agree with anniebrooke. I also want to encourage you to get used to discussing things that go on with your lady parts without embarrassment. :>)) Everyone has genitals and it's just part of life. Your mom will want to help you as I would want to help my own kids. She's, after all, got a vagina too. :>) And doctors discuss vagina's and bumps and lumps and smells and discharge on a regular basis. They think nothing of it. So, just see it as another part of your body you have to take care of and let the embarrassment part go. good luck and come back for your questions, we like to help!