Exercising everyday however not losing excess fat, something wrong?

Patient: Hi there,i am 16 years old and i am a competitive squash player. i play upto 1 and a half hours 6 times a week and i also have a fitness programme that includes 3 aerobic sessions and 2 strength sessions. i am quite short at only 153cm and weigh 52-53 kgs. im not exactly fat but i do have rolls on my back when i wear a bra and my stomach isnt as flat as it should be. i do not know why i have that fat on me as i am so active and why it wont go away as i eat very healthy and exercise so much. all my friends and squash pals are much thinner although i work harder. both my parents are thin. also i havnt grown in the last 3 years (i still only wear an A cup or AA) and my periods are VERY irregular -they come every 10 months for the last 4 years. i also have constipation. i am at a loss. i have tried so hard getting rid of that fat, and it affects me so much mentally and emotionally. but i was just wondering if i may have a problem? PLEASE HELP ME. both my parents do not have throid problems and i also have low iron. also i gain weight quite easily, for example i weighed 49kg a month and a half ago and i am already 52 even though i have continued with the same fitness routine.