Why am I spotting?

I've been using birth control pills the last two years and lately I have been taking it few hours then the time I'm supposed to. And when I have intercourse with my boyfriend he usually just withdraws. Is it because I'm not taking it on time to have spotting? Or is it because there's a chance of being pregnant? I'm supposed to be on my white pills the next few days and I usually don't get any spotting.