Period while on the pill

So I just started taking the pill and have taking it pretty consistently (only being late by either a few minutes of a few hours) and my period was late by 4 days and my mind went straight to pregnancy since I had sex with my partner on the 16th of this month.. he didn’t ejaculate inside me but there’s always a chance right? Anyways I just started taking the placebo ones in the pack and my period came but the blood is darker than usual almost looking brown and there’s isn’t as much blood as I’m used to.. but the abdominal cramps have been insanely painful when the point of me getting on the pill was to alleviate the pain a bit and also have a line of defense during sex.. is this normal or am I just overthinking