Any advice?

I got my period a day late this month it’s light and it’s a mix of blood and brown (the old blood at the end of your period you always get). It lasted for only 2 days. My periods are always on time and extremely heavy and I never get the brown old blood until like the last day of my period. I always have my period for 5-6 days. I just think it’s strange to be getting the brown blood at the beginning and all through my 2 day period if you would even call it that it’s never happen to me before. Idk has this happened to anyone else? Does it mean anything?

I did have unprotected sex and took a test a couple days before I was suppose to get my period but it was negative. I’ve been feeling nauseous every morning for over a week and one day my boobs were really sensitive.