Continuous break through bleeding after 1+ years?

I'm currently on a three month supply of a generic brand of birth control, called Junel. I was prescribed this in March of 2010 and have been religiously taking it when I'm suppose to. Most recently, about a month back, I started an odd cycle of break through bleeding which lasted about 3 weeks. It's dark brown, with stringy clots. I then ended my three packs of pills and got my period, then started back up again one week after (like I'm suppose to). Two weeks later, I started having uterus cramping and also some cramping in my cervix and just today, I started bleeding again. My last pack of pills isn't suppose to be until August, meaning I am not suppose to get my period until then, yet I am continuously having breakthrough bleeding. I have not had any stressors, nor has anything in my diet changed so I am very concerned about this. I am using up a light tampon every 5 hours (which is very much the same as my normal period) Any ideas as to why my body has been bleeding so much?