Can I get pregnant from switching my birth control pills and having unprotected sex in the first 2 weeks?

I was on Nortrel 1/35 and switched to Tri-sprintec. I waited until the placebo week was over and then I started taking the Tri-Sprintec on Sunday. I had unprotected sex in the second week of the Tri-sprintec. How possible is it that I could get pregnant?