Ok i am 16 years old(just turned 16) and i have never gotten my period before.?

ok i am 16 years old(just turned 16) and i have never gotten my period before. i turned 16 in june and i went to a doctor about it and they said to come back after turning 16 but i never did. yesterday i had a paniliner on because i was wearing white pants and when i went to the bathroom there was a lot of brown discharge in the pantiliner and it even leaked through to my pants (thats how much there was) and today i had gymnastics from 9 to 2 and i put a tampon in so it wouldnt leak through to my leotard and when i took it out it was all brown. is this finally my period???