Did I miscarry? Please help :(?

Ok, here is the back story. My LMP was 4/13-4/17. On 5/8 I had a very short light pink period that lasted 3 days. I was on BC the whole time, I did miss a few pills though. I thought that the early bleeding was either breakthrough bleeding or implantation bleeding. Well, I quit my BC just in case. I took 4 preg test. 1st-Day of early bleeding, Neg. 2nd-Day period was due, Neg. 3rd-5 days after that, Neg. 4th-2 weeks late, Neg. After all the Neg tests, I started my BC again. The past two days I've had horrible upper stomach/lower back pains. I thought I was dying honestly. Well, today they stopped and I went to the bathroom and saw that I started. Which is about the right time for me to start. Well, when I took the tampon out, it was black/bright red blood and covered with two grey and pink tissue globs. I called my DR. immediate and she said to save them and bring them in tomorrow for testing. She said it's probably a miscarriage but it could be loss of lining from going off and back on the pill. What do you think? I'm terrified! Thanks!