I'm only 17 and two weeks ago I had the same problem. I was embrassed to tell my mom, so I thought that it was nothing but it started to get bigger and I started to have pain sitting and walking. And it turned out to be bartholin so I told my mom and with her help she called the doctor got me the antiaboitics that I needed. So don't be embraced to tell your mom because it's scary going throw it alone not knowing what's wrong with you.
There is nothing to be embarrassed about! I remember when I was in high school and I had a yeast infection and I went to the store and bought some Monistat (which is expensive) on my own and my mom found out. She just asked me why I didn't tell her! She explained she would have taken me to the store and bought it for me if I would have just asked :). Moms understand "girl stuff" can be embarrassing and confusing and scarey. If you have a history of cancer in your family your mom would probably want to know what's going on anyway! Now, I HIGHLY doubt what you have is cancer. The post before me is right it is probably just a boil or infected hair follicle. If it is concerning you just talk to your mom and go see the doctor. You will get it all figured out! It will be just fine!
It could be a cyst or a boil, neither of which that is particularly dangerous. If you shave, it could be a hair bump. It may go away on its own, but I would talk to mom about it and see the doc to confirm what it is and what you can do to be rid of it.