birth control, ammox, and broken condom

i have been on orthro tri-cyclin for 4 years without a break. i also am taking ammoxicillin for a sinus infection. last night my boyfriend and i had sex but the condom broke.. what is the chance that i could get pregnant? i tried to get the plan b pill but the pharmacist didnt want to give it to me bc it was too much estrogen. does anyone know the likely hood that i could be pregnant? im just freaking out a little.