Spotting Mid-Cycle

Basically, I'm on the pill, and I have been for a little over a year. I always have my period on the days allotted, but since August I have been spotting for two to three days about a week or two before my actual period. 
Should I be worried or is this normal? Does this mean I should change my birth control? I can deal with the spotting, im just worried that the pill is les effective? I don't know. Help!?