What Causes A Repeat Period With Stomach Cramping After Intercourse?

I missed my pill, I take Triviora, on the 28th of this month. I had sex on the 29th and did not use any other birth control. I can't find my pills and so haven't taken one since. I woke up yesterday with my period, even though I just had it a week to a week and a half ago. I have also had cramping in my stomach since yesterday. Should I be worried and about what?