Why won't my period stop!?!

So I have been on the same birth control (ortho tricycline-lo) for about 3 years now with no problems. For the last 3 weeks, my period has decided to pay an unwanted visit and stay-cation. I have never missed a day of my pill and this is all occurring during the time where I am not supposed to have my period. Does anyone have any suggestions on what might be happening to me or what is causing this? I still feel healthy, I just have my normal cramps and bloating. I just want answers because I feel like I'm starting to lose a lot of energy and want to do basic every day tasks.