Curious!! Help!

Courtney
So, me and my boyfriend have been having a lot of sex. I've been on birth control for a few years now. I take it every day around the same time. Always. I rarely miss a day. 
Since I'm on birth control, my boyfriend likes to cum inside me. I know that birth control isn't 100% effective, but I know that as long as you are good about taking the pill, you're mostly safe. 
Today I started my period. At least I think I did. I've been cramping but usually my menstrual flow is very heavy when I first start; like, it's so heavy I have to change a super tampon in a couple hours. This time it's light. And that just really concerns me. Am I spotting or is it actually my period? Is it normal for a menstrual flow to change? Am I freaking out over nothing? Lol