Concerned

So I'm on birth control and have been since December, I have 3 active pills left until the inactive pills and I usually start my period on the third inactive pill. For the last hour I've been having cramping like I'm going to start my period and lower stomach pain, and I just went to the bathroom and there was a little bit of blood, do you guys think I'm starting my period? Shouldn't my body be on. A schedule by now? Is this normal?