Thank you for writing!
You don't say what method of birth control you are talking about.
I don't know what you mean by "would it would be effective one time?" - do you mean would it be effective straight away? Condoms - yes. Regular birth control pills - no. And you need a prescription for the pills.
If you want to go on b.c. pills, my advice is to wait until you stop bleeding and then start with the birth control pills. Use condoms until you have been on the Pill for at least 5 days.