I've Had My Period Last Week (it Ended) Last Night

I've had my period last week (it ended) last night after swimming I had a nickel size blood clot then it was pink and today it was brown I also am not sure how to figure out my period schedule because I never know when it starts or if super light counts because the next day I might have nothing also I've never been to a gynecologist before and I'm turning 19 in November