What Causes Irregular Periods And Burning While Urinating?

okay, so im 15 years old and weigh 95 lbs. and have had 2 periods, they are so irregular.. its annoying. they have been 3 months apart and now 4 months later, i had a period, or what i think was one, but everytime i pee it burns soo bad. whats wrong with me? i have been looking up stuff about it uti's online and i was wondering if it was a period, a uti, or something else.. plz help :)