Miscarriage?

So on nov 27 I took a plan b. My period wasn’t supposed to start until the first week of December but it started nov 28. I bled for a week regular/light n it stopped for a couple of hours n that same night I started bleeding again but super heavy. I’ve been bleeding for this past week really heavy n now I’m on my third week it’s getting light again. Could this be a miscarriage my dr is going to get me an ultrasound Saturday but I’m so nervous I’ve never had one before. I had been feeling nauseous but I always do with my periods and my breast have been sore which is also normal during my period and I have been having little pains on my lower belly which I never have I usually get light cramps but these feel more sharp I guess. I did have sex on the 27 the day I took the plan b n my bf did cum in me that’s why I took it. Do y’all think maybe it’s the plan b that caused this n it was just my period heavier. Or could it have been a miscarriage :( I just went to pee and it’s just brown discharge nomore blood