I've been bleeding for 13 days and I'm worried it could be a miscarriage. HELP!?

I have had a steady boyfriend for about 4 years and we have regularly and typically my period always comes on time and I take the birth-control pill yasmin. However this month my period came a few days late and was extremely heavy bleeding through a tampon in an hour. For about 4 days it was like this. Now ive been bleeding for about 13 days tomorrow will be 14. The bleeding isn't heavy like a period its more like spotting but its brownish and clot like or bright pink the color changes daily. Ive been experiencing extreme back pain abnormal cramping abdominal pain. Does anyone have an idea what this could be?