When taking birth control pills,breakthrough bleeding
might occur in a small number of females.
You should meet up your doctor and ask him/her to suggest you birth control pills of a different brand.
This usually happens when your body adopts to taking a certain kind of pill.
Sometimes,such a bleeding may occur if the time of taking the pill varies.
As you have mentioned that you had very scanty periods this month,i advice you to rule out pregnancy
as 0.01% of females on birth control pills have been reported to conceive even when on pills.