AM I PREGNANT?

Hey y'all. I had sex on the 28th of February and it was the last day of ovulation. He came inside me and I took the plan b pill that same day. My next period was supposed to arrive on the 14th of March, but on the 9/10th I had light spotting and mild cramps. Took 2 home tests yesterday and the first one was invalid while the second had ONE very clear line. I haven't had my period yet and I'm confused. Please help!

UPDATE: I forgot to add that February was one month I really took the plan b pill.(Three or four times that month). I've never taken it that much in one month. It's the 24th of March and there's still no period.