What Are The Chances Of Pregnancy Inspite Of Being On Birth Control Pills?

HI, i am wondering if i could be pregnant. I had sex a week befor my period and i started early and stopped earlier than usual, if it even was my period. I have been having some symptoms of pregnancy but thought they could be just from stress. I had unprotected sex. I am on birth control so my period is always on the same time. Could i be pregnant?