Help!

Okay so i’ve been on tricyclen low for 8 months now and this month ive been having some problems. The last 4 days ive been light bleeding/dark discharge, a part of me thinks its from taking my pill later on after im supposed to since ive been working alot i always forget to and end up taking it later. I have 2 more active pills in my pack than im supposed to start my period. What is this?