What Causes Brown Discharge?

Hi, I am 24years old and I m a married women. I have been taking tab Femilon for 4months. Because I was having irregular period. But after starting taking Femilon my periods are now ok but I have been facing another problem. I m having brownish discharge, and I don t know the reason why? I m so worried about that. Please tell me should I stop taking this medicine or should I continue on it?? Is it safe to take Femilon? Doctor advice me to take Femilon for 1year.