What Causes Irregular Periods At The Age Of 14?

since i have been a child i havent come on my periods properly i started when i was 14year and would come on soo little that i could barely see it i never had any pain or cramps to know i was on after telling my mum i went to a lady Doctor and she told me it was because i was very overweight and put me on the birth control pill take it everyday for 3 weeks then don't take it for a week i came on my periods properly for the 3 months i had the pills then back to having hardly any period. My Question is the week i came on my period after not taking the pill was it a real period or a fake one? someone told me it sill wasn't me having a normal period because it wasn't natural and can you tell me the risks of me not having a period will i not be able to have children i am getting really worried.