I have been taking bith control pills(sesinque) started them on march 2 2011. I stopped taking them on march 26 2011.. my period came on 5 days later which was on mrach 31 2011.. I had unprotected sex on April 15 2011... could I be pregnant?

Yes,

1. even if taking the pills currently, they are not 100 percent and you could be

2. if you even miss one pill while taking them, it makes them less effective.

So yes since you were off them @ 3 weeks or so, it increases the odds greatly.

Since you stopped taking them, I will assume you are no trying to become pregnant, so good luck