It could be either a miscarriage or my uterine lining is all expelling in one big chunk

I'll start by saying I apologize for all the graphic detail I'll be getting in to. I just started a new birth control about 2 weeks ago and my boyfriend and I had unprotected sex.....can't remember if I started the pill before or after. My package insert for my birth control stated to take the first pill the day I started my period. I started spotting and took the first pill thinking I was starting my period and as soon as I took it my period stopped. I've always had very heavy periods with lots of clots, bloating,  and cramps that make me sick to my stomach. Lately, I've been spotting for a day or two before I get my period....I'm guessing it's because my body was adjusting to me discontinuing my last birth control. After I started this new pill a couple weeks ago I wasn't bleeding the first week and the second week started spotting. I got nervous that I wasn't getting my period yet and thought maybe it was due to taking my pill and it was messing up my cycle. As soon as I stopped the pill a couple days ago I got my period. It's been light the past two days and like I said I have always had heavy periods. Today it got heavier and I thought it was back to normal because I started cramping. When I was heading home from work the cramps turned into a sharp constant pain that covered my whole abdomen. It felt like I had to use the bathroom and *excuse me for this* pass a bowel. I stopped at the closest drug store and used the bathroom. I only had to urinate, but a couple normal sized clots came out. The pain was still there, which usually mean I still have a clot that needs to come out. So, I wadded up some toilet paper and reached up and I got another normal sized clot. I was still in pain so I waited and a minute and something else came out. It was about 2 or 3 times the size of the clots and it looked like a giant clot with a pink flesh-like substance  in it. After that came out another tiny clot came out and the pain was gone. I feel physically ok now.....just a little scared and stressed. I googled it and asked a friend. I've gotten that it could be either a miscarriage or my uterine lining is all expelling in one big chunk. Has this happened to anyone else???? Any response or feedback would help greatly!!!