Dark bl

Hey guys!! Please don't judge, I didn't know where else to go!! I lost my virginity last month on the 12th... I had sex a few times since then, once being unprotected, I was off the pill because I'm switching to different one due to hormone imbalances. ANYWAY... I was really worried because my period is always on time and this month was 7 days late, it started today and was a dark brown color, very thick, and painful.. I always have painful periods, but never this bad... Can you answer why it's brown, and so pai