Do not worry. This is likely to be the side effect of I pill. If it happens in next months, then you need to have some tests and gynaecological consultation. Otherwise no problem.

Hello, nothing to worry, I pill contains high dose of progesterone hormone it causes shedding of endometrium to prevent fertilized ovum to get Implant in uterus. These shedding comes as menstrual bleeding which can occur any time from four hour of taking tablet to 1 week. Next few bleeding may be irregular, may come early or may delay. No need to worry, it will normalize itself with in few weeks. Barrier contraceptive methods are always better choice over ipill.