I think you're supposed to wait at least a month or two for them to be 100% active in your system. But sometimes it takes a few days to start your period when you've reached the end of your pack(and starting the sugar pills) I am on a 21 day pill pack and of the 7 days I am off them I only have 2-3 days of period (so about 3-4 days after I stop taking them)
Also JUST starting the pill will most likely mess up your cycle the first month. So give your period a chance to show up and before you start your new pack, you still haven't gotten your period, take a home pregnancy test to make sure. I remember when I first started the pill I didn't get my period at all.
But you should be using condoms until you reach the end of your next pack JUST to be sure or have him pull out before he ejaculates at the very least.
good luck