When is it ACTUALLY ok to have unprotected sex when on birth control?

So about two months ago, I was put on a low dose birth control. The doctor says that it only takes 7 days until you can have unprotected sex, but my sister says it takes 6 months before it's fully preventive.

My boyfriend and I both really want to have sex tonight because we haven't seen each other in a while. He likes to finish inside, not out.

Is it ok to do that??