The time it takes from infection to illness for each sexually transmitted disease (STD) is different. It could take days to several weeks. Most STDs show no symptoms at all, which is why testing is so important.
You could be exposed to a STI by sexual contact or exchange of bodily fluids (blood, semen, or vaginal fluid). Condoms are very effective at preventing most STIs, if used accurately and during every sexual encounter. STI testing is recommended every 6 months if you are sexually active or when you have a new partner, because many times you don't have symptoms when you have an STI.
If you think you have been exposed to an STI talk to your Health Care Provider to see if testing is recommended for you.