Long periods?

I've been on oral birth control for nine years now with no issues, but lately my period has been abnormally long and not matching up with my birth control (I take the three month pills. My doctor attributed this to my thyroid levels being low, but I've been on the thyroid meds for months now and the levels are pretty much normal now. Today is day eight on my period and I'm going through a super tampon about every two hours. 😭