I wouldn't worry about it too much. There are very few cases of stds spread by fomites (inanimate objects).
Most stds do not survive very well outside of the body, especially in dry environments.
I am not aware of any cases of HIV being spread by fomites. The virus is simply not a good survivor in dry environments. Neisseria gonorrhea or chlamydia may survive outside of the body for a few hours, but once again, they live shorter in dry environments. Theoretically, HPV (genital warts) could be transmitted and is probably a better survivor, but this is a rare mode of transmission as well.
In summary, I wouldn't worry too much. If it were me, I'd just watch for any signs of infection: burning while urinating, urethral discharge, skin lesions on that area.
If it will ease your mind, you can just go to your primary doctor and say you are concerned about stds and would like to be tested; he should happily oblige.