Yep, this is similar to what happened to me. I was bleeding every two weeks but bleeding sometimes went for 8 days other times just 3 days. The start of the bleed was also getting closer and closer, so i was bleeding more days than i was not.

I was well sick of it, and got a script for an alternative minpill, but when i looked at the ingredients they were pretty similar so i hadn't filled the script yet. I was looking into other contraceptive options - and then i got pregnant (while tandem feeding and continuing the minipill). I don't know if the bleeding made the minipill less effective, or if i am just a super ovulator, but i won't be taking it next time and will look for something else.

My GP was very unhelpful so i don't have any medical info on what effect frequent bleeding has. I also found little info online other than change contraceptives if it is annoying you, but did not expect pregnancy.

hth