Stephen has a burning sensation during urination and has noticed a yellow-white, pus-like discharge. which sti matches these symptoms?

The Sexually Transmitted Disease (STD) which matches Stephen's symptoms is gonorrhoea.

Gonorrhoea is caused by the bacterium Neisseria gonorrhoeae. It is an STD which when left untreated, it can spread and infect the joints and heart valves. In males, the symptoms include a burning feeling during urination, a yellowish discharge from the penis and pain at the testicles. In females, burning during urination, vaginal discharge and bleeding during periods and pelvic pain.