I get my period 3-4 months at a time. why? is there something wrong?

OK to start off with i am 15 years old, and i am a freshman in high school. i cant really remember when i started my period. i know that it was in 7th grade, and that it was Friday the thirteenth. but since it there are two Friday the thirteenths, so i don't know which month i started it on but i know i was 13 so yea. i don't really get cramps on my period, but a few days before i do get my period i start to feel something in my lower abdomen area. anyways so i dont get my period for 3-4 months at atime. i heard being stressed can cause this, idk i might be im not sure how i know im stressed. i dont really want to go to the doctor's because its embrassing and i dont likeing talking about my opersonal thngs. but if it is something to worry about i would. i have never had sex in my life, i belive in sex after marriage so none of that bull****. i feel normal, nothings wrone. i am overweight, but other than im okay. im worried, my mom's worried about why im not getting my freaking period, its annoying wondering when its gonna come. i know that it has been two years but between those two years Ive only had a few periods, and they last between 5-7 days, someone told me that those are probably not your real periods, and that your probably not ready yet, i don't believe that. what should i do. i know that i am a teen, but this doesn't seem irregular to me.