What Causes Light Period Inspite Of Being On Melodene?

Hello. I have been on Melodene for the last 8months with no problem. Then when I got a new packet I completely lost where I had been and made an educated, possibly mistaken, guess. Now for the last 2 months my period comes a week before the red section of the pills. What should I do? Stay where I am? Skip agead to the red section? Please help me