Monthly breakthrough bleeding on BC pill?

I have been taking microgestin 1/20 fe starting 2007. I got pregnant in 2009. After my baby was born I started taking it again last Aug. Ive.been on time but.for the.last couple months ive been having my period about 4 days early. With cramps & all. It sometimes only lasts a day or 2. Is it time for a different pill? Coincidentally I had sex last night and woke up to the.period, could the sex have triggered it this month? what do you guys think?