I messed up my birth control and started a new pack. when i took the first week, i bleed for 3 days. now i am confused when my period will come again.

Placebo week: When you bled for 3 days, that was likely when you would have had your period with the previous pack of pills. By starting a new pack of pills, you reset your cycle, so your menstrual period will likely occur during the placebo week of your pills, I.e. week 4. If you are using a 21-day pill pack, your menstrual period will occur at the completion of the 21 pills. Hope that helps.