antibiotics and birth control

I was prescribed Amox-Clav penecillin for 14 days twice a day for sinusitis. I take my birth control pill religiously. I had sex tonight multiple times and each time he pulled out 100%. I know precum is existent but I know no ejaculation got in me at least. I'm on my "period" and bleeding, but I'm taking active pills (my cycle is screwedd up for now) I didn't know at first they would affect my birth control that badly. Should I take plan b?