Plan B

I'm fifteen. My boyfriend and I had sex, and we're always very careful to make sure the condoms are on properly, but this time the condom broke. I took Plan B within an hour and a half of it happening, but I'm still scared. I've been on birth control for a week plus the Plan B pill, and now I've got no idea when my next period will come. Is there any way to tell whether or not I'm pregnant before my next period? I'd really like the peace of mind.