This sounds like a urinary tract infection. Bacteria can get caught inside the shaft so it's best to see a doctor and get antibiotics before the infection moves into the kidneys. You may also be feeling tired or washed out or fatigued. Low grade fever, pain in the waist , side or back. Also yeast can be a culprit as well. Guys just call it jock itch. Either way let a doctor know you are not sexually active and they can run a culture to determine the cause . With antibiotics, you should feel better in a few days.Pain and burning are also signs as well as slow urine flow.
I wouldn't worry too much about an STI and you are still fertile.
Just let the doctor know you are having some issues