Talk to Gynecologist on Unusual Period Cycle

AoA I am a 16 years old girl my menstrual cycle is being usual since 8 to 9 months now the length of each cycle is 21 days and bleeding day consist on mostly 8 to 9 days with light bleeding in strat and heavy at the end. I don't feel any bad cramps or other things. but back pain is a little hurtful. even without in periods I sometimes still feel pain in my lower back. I hope there's nothing special.