Hi, I m 18 years old and this is my second month on the pill now. I m a few days into my 3rd week and I ended up with a UTI and was put on a course of trimethoprim to take one twice daily. I started them on monday, i m due on my period thursday/friday. I have only just found out that it might decrease the pills effectiveness and i m worried that i may be pregnant as my boyfriend and I have had sex twice with no protection. is there a definite possibility that I am pregnant? Please help.