Do you have any other symptoms? Pain, burning, itching, anything?
You could have a urinary tract infection, urethritis (an infection in your urethra), an infection in your prostate - all which can be caused by other things than STDs.
How long has it been since you've been sexually active, including oral sex? Most men who get symptoms will get them within a couple of weeks after infection, depending on the infection, and it would be unusual to get them much later, but it's possible.
What does the discharge looks like?