Period or pregnant?

So, my boyfriend and I had unprotected sex on the 27th of February. I panicked afterwards for no apparent reason, like always. I took a Plan B. My next period isn't supposed to start until the 20th of this month, but for the last couple days, I've been kinda spotting. To me, it isn't really really spotting because it's only when I wipe and it's just a pink tint. My periods have never been regular and just month it started just like this but only 2-3 days early. Most of the time they're late and I NEVER spot like this. He keeps telling me I'm not pregnant and that there's no way I could be. He's probably right, but I've just been really nervous about it, like to the point where I can't sleep. Please help.