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.
https://www.healthline.com/health/male-discharge-non-std
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?