Is intercourse taken before taking an antibiotic protected?

Hi I have a question about contraceptive pills vines. I mean, I started taking the antibiotic zinnat. (September 18) However, I know that it can weaken the contraceptive effect. Is it possible to fear pregnancy when the last intercourse took place on September 13? I will add that I use the tablets regularly and I have not forgotten any. Also, there was no vomiting or diarrhea.