Started Birth Control, Had Intercourse Between First And Second Pack Of Pills, Observed Heavy Clots After Second Pack. Miscarriage?

Hello. I started taking birth control a few days before I was supposed to get my period. I was visiting my boyfriend so I decided not to wait for my breakthrough bleeding in between the first and second pack of pills as it would have inconvenienced the both of us. I just finished the second pack 2 days ago. At first I had a bit of brownish bleeding so I went to sleep thinking I would get my period the next morning. However, the next morning I had incredibly painful cramps , like never before, I took some painkillers and went back to sleep. When I woke up, I went to the toilet and as soon as I sat down I discharged a heavy, round, bloody clot(?). I was worried about having had a miscarriage but my last sexual intercourse was 2 weeks ago. Is this happening because of the 2 periods I didn t allow by taking birth control or should I be worried?