Can I be pregnant if I have a cold while taking Vines, drank Theraflu and became stressed?

For more than half a year I have been taking vines birth control pills - always on time, I do not skip the tablets. At the beginning of the month there was a strong cold, I used the drug Theraflu about 2 sachets per day. On February 13, there was an intercourse without a condom, but there was no ejaculation in the procession. Before the withdrawal bleeding itself, the "cold" developed into pharyngitis, and I was also accompanied by stress. Bleeding only appeared when taking 4 placebo tablets and lasted less than three days. I did two pregnancy tests (7 and 8 days after that intercourse) and both came out negative. Is there still a possibility that I'm pregnant? I was worried that the disease and the medicines I was taking might have affected the effectiveness of contraception. I would add that the day after the second test, I started taking an antibiotic under the cover of a probiotic, because of the disease. Here the second question - how long do I have to be careful because of the reduced effectiveness of contraception? thank you very much in advance for your reply:)