Could this be a miscarriage?

I just switched birth controls about 3 months ago.. the first two months were samples so they were free. After my pills ran out i skipped a week of pills because i had midterms and between cl and studying i never found time to make my way to the drug store.. the following week i filled my prescription and found out it was 60 bucks so i decided to wait until my mom ok'd it before buying.. which was the Monday of the next week. Within those two weeks of not taking the pill I was ually active. Now I've been taking the pill for two weeks. Almost a week ago I missed a pill and the next day I had a good amount of very dark brown (almost black) chunky discharge in my panties.. sometimes when I miss a day ill have slight spotting but nothing like that.. I've continued taking my pills on a daily basis.. yet I'm still bleeding(about 4 days now). But none of it appears to be fresh blood. It's all clots and occasionally clear-greyish stringy like discharge will come out too. This is really abnormal for me.. Could it be my body trying to have my period at the correct time? Or do you think miscarriage? I've also been cramping in my lower abdomen more than usual. Thanks for your help!