Sounds hormonal to me, it would be wise to discuss this with your GYN or GP to rule out anything serious and to possibly have a change in meds.
Sounds like your pill isn't doing the job any more, and you've got breakthrough bleeding. If you have sex before changing your prescription, be sure to use condoms. I wouldn't worry, our bodies do change in terms of how much hormonal activity they naturally have, probably you just need a higher amount of progesterone in your pill.