help please!

I lost my virginity last Saturday night (9/14) and had some light brown discharge the next day but no pain when peeing or anything like that. Today (9/20) I just randomly started my “period” even though I have 7 days left until it’s supposed to start. It was very dark brown in color and only lasted a couple of hours but my periods are typically super regular.

I don’t have any cramps or pain of any sort so I’m kind of confused? I feel like this is normal but I thought I would ask here for some extra help!

*I did just start taking my bc at exactly 10:00 each night instead of just taking it whenever at night but I didn’t switch medicines or anything. Not sure if this caused any hormonal imbalance.