I am on the pill but was recently given antibiotics but wasnt told that these could affect the contraceptive pill. I had sex with my boyfriend on the first day of taking my antibiotics and then found out about the affects, i havent had sex since but had to run my pill through as it was due to finish while was still on the antibiotics. This was 2 and 1/2 weeks ago now and on Monday i started to get a brown discharge on and off and also have had period cramps and back pain, i am really stressing but cant take a pregnancy test for another week. What are the chances of me being pregnant?