What Causes Early Period With Some Spotting And Brown Discharge Before Period?

I have been on the same birth control pill for the past 17 years. I took a break for a year and then started again. I have had a regular 28 day cycle for 17 years. Even when I wasn't on the pill. For the past few months my period has been coming early and early. I have also been experiencing spotting and brown discharge a few days before my period starts. I have not been sexually active for 2 months. I have taken two pregnancy tests and both were negative. This month I have just had an almost black like discharge that is very light instead of a period. I am concerned about the irregularity of my periods