Did I have a miscarriage?

I'm on the birth control pill seasonique so I only get a period every three months, but a few days ago I got very very dark spotting and it stopped for a few days and then it came back and I've noticed dark grayish clumps after I go to the bathroom you know? I looked this up and it came back as possibly a miscarriage. I have had some abdominal pain but I'm not extremely healthy so I didn't figure anything of it and because my fiance and I are so careful about using protection every time I didn't think anything of it when I felt naseaus every now and then. I just started cross country training and my appetite has decreased enough this week that my fiance is really worried about me. I feel fine, I just haven't been really hungry. Any similar experiences? Oh and back pain, my back's been sore.