plan b?

I was on an antibiotic for 10 days for a sinus infection. I've been taking bc religiously for 3 years, but the pharmacist said to use a back up method of bc while taking the antibiotics. When I was taking them, I had sex twice, once unprotected. I started to worry but I did a lot of research & every single article I saw said the only antibiotic that affects your bc is one to treat tb. I was still scared so I took a plan b along with my birth control.