I ve been taking birth control for close to two years now. Recently, my doctor prescribed cephalexin for a minor infection. I know that previous antibiotics have messed with my birth control. I take my birth control regularly and at the same time every day I bought some spermicide just in case cephalexin did mess up my birth control, but I forgot to use it today. What are the chances that I could get pregnant? I m a healthy weight an height, and I ve never had any reproductive problems that I know of. Should I consider going out to get Plan B?