no period, ever! need answers

I'm 20 years old and never experienced a menstrual cycle (period) only when i was 15/16 i had light spotting that lasted one day. Wednesday of last week i had sexual intercourse, next morning i woke up with heavy bleeding. I'm not sure if it was my first period or something else. It stopped today, i had sexual intercourse today and after sex it has returned. I've been going to the endocrinologist and they're trying to figure out why i haven't gotten a period yet, they don't know about the bleeding yet because my next appointment is in november. I made an appointment for the gyno next week, i would like to know if it is possibly my period or another medical condition?