Period? Pregnant? Other?

So for a few days before my period was supposed to come I had different symptoms. I didn’t think anything of it though. Just sensitive breasts and slight food aversion. I’m on birth control though. But then, my period(?) came and it was way different. 4 days, DARK brown blood and way lighter than my period but could fill a small panty liner and one day in the shower I noticed lots of cervical mucus(?) and now my period is practically over but still dark cervical mucus and I’m confused.