I'm 18 , I started using birth control 3 weeks ago.. I started the both control the week after my last period but the fist week I started taking the pill my boyfriend confessed that he didn't pull out and we weren't using protection.. The next week I had another period that lasted for 8 days.. I really don't knew what to do.. Would the birth control be effective after only 1 week and why did I have two periods in the same month and why did my last period last 8 days that has never happened .

No the pill would not have any effect after one week. Not sure why additional bleeding.
You will need to just wait and see if you get next months period.

Birth control can cause changes in your menstrual cycle. Some women experience constant bleeding. The pill can cause extra periods, especially in the first month or two while your body gets used to the added hormones.

If you're worried, take a home pregnancy test. It can take up to a week for the hormone levels from the pill to build up enough to be effective, so pregnancy isn't impossible.