Can Medication Taken For Endometriosis Lead To Heavy Bleeding?

hi,
I was diagnosed with endometrosis in march and this was confirmed after i had a laparoscopy now some of it was removed but my doctor has since put me on a pill that i must take for 3months without a break and then stay off it for a week to let my period come but i am currently only near the end of my second packet and i have had constant bleeding the last two weeks with alot of pain. My periods are heavy too each day and they don't seem to be getting any lighter. i haven't missed any day with the pill and i take it regular each day. I'm just really concerned this isn't normal could you please help me ,
Thanks!