so i think this is where my question goes, so sorry if its not!

my last period was right on time the 12th, but it was only one day of really heavy bleeding and then about 2-3days of the dark brown old blood. it’s concerning because ive heard things like that happen if you are pregnant? i know i cant be since i havent had sex, but i have fooled around with my boyfriend (been dating 2+ years but have NOT had sex yet. we are both 17) - so my question is , is this normal for a period???

and i know people are going to say “you need to educate yourself before you do anything” so please dont reprimand me or yell at me. i am just concerned for my period and im asking people older who would possibly know. thank you!