What Causes A Heavy Period While On Nuvaring?

bloody discharge
I'm a 23 year old female on Nuvaring...my periods have always been regular. Recently I was bleeding for 3 weeks, too heavy to wear a panty liner, but heavy enough to wear a pad. I notice that with this, I did have some clogging, which some of it was thick and looked like actual skin. I just wanted to know if this was normal and if not, what can I do go change that. I should also include that I have had a pap smear in the last 3 months.