When do I begin taking my birth control pill if my cycle has come and ended already?

Talk with your. Prescribing dr about how they want you to proceed but there is no reason you can't begin at almost any point in your cycle depending on the prescription you are taking.

Related Questions

My cycle has just gone over 100 days. I have polycystic ovaries (not syndrome). Recently stopped birth control pill. Is this detrimental to my health?

Not really. Will not affect your health; however, keep getting screen for ovarian function and diabetes. Read more...
No, but see your doc. You mention you're not sure if your pregnant. So doing a home pregnancy test would be helpful, and calling or seeing your OB/GYN or PCP would be good. So they can follow you on this and keep a record on you. Read more...