What Causes Nausea And Pain In The Pelvic Region Post Menstruation?

I had 3 positive pregnancy tests, I started having normal period symptoms but with much more pain than normally, I started getting huge blood clots mixed with hard pieces of white skin, I retook a test and it came back negative, now (almost 2 weeks later) I have strong pelvic pain and I feel Nauseous at times, what is wrong with me?