It could be a urinary tract infection or a yeast infection. They could come from masturbation if you are doing something that targets the urethra (don't put anything up it, for example) and especially if you touch yourself with your fingers without being a thousand percent scrupulous about washing your hands really well before you masturbate. The hands actually have more dangerous stuff on them than your lady parts do.
UTIs can be addressed by home remedies, though sometimes they need more. Try doing some sitzbaths (sit every day for ten minutes in a shallow bath in a tub -- toss a little bit of white vinegar in the water if you have it, but not too much), and/or you can try drinking cranberry juice every day to increase the acidity of your urine and knock it out.
It could also be a yeast infection or fungal infection, and luckily there are treatments at the drugstore that can help if so. Your mother should be able to help you there -- and you don't have to admit you've been 'doing the deed' either, since women get yeast infections from other things besides masturbation. They're really common.
But if nothing fixes it, do see a doctor. He or she can diagnose the problem easily by doing a swab and sending it to the lab, and of course will be able to prescribe just the right thing to solve it.
You should always see an obyn when you have new sx. Leaving an infection untreated will let it harbor in the body undetectable and contribute to an overall pathogen load that cause decreased quality of life as diseases silently progress, contribute to 1 in 9 people who get kidney failure, for example. Just get it checked out. You are at the age where regular checkups, 1/year are needed. It's a good opportunity to get established with your own obgyn. If not available, Planned Parenthood is a good option. Good luck!