My period ended sept 3 and i took my first bc pill on sept 4. today, sept 12, i started bleeding again. i thought bc was supposed to regulate periods?

Breakthrough bleed: Breakthrough bleeding (bleeding at the wrong time) is very common on birth control. It happens in about 1/3 of users. Its no big deal and usually self corrects over time. If you are not satisfied or it continues to happen then consider using a different birth control method. It is a common side effect and does not mean something is wrong or that the pill is not working.

BTB: You might be having some breakthrough bleeding, which is fairly common with low dose birth control especially the first cycle pack. If it doesn't improve in another pack or so, your physician might want to change your pill to one with a higher estrogen dose.