I am on the implant have been for over a year now i've been bleeding really heavy for two weeks with bad cramps and back ache i've also passed clots?

Breakthrough: Sometimes patients will experience breakthrough bleeding when they are on a progesterone only method of birth control as it can cause the endometrial lining to become very thin, and can result in bleeding. This can at times be as heavy, or heavier, than your menses. Pregnancy should as always be ruled out as a cause. You should follow up with your gynecologist for further recommendations.