A couple of months ago I received unprotected oral sex from a female sex worker. 25 days later I started having a burning pain in the tip of my penis, but no discharge. I was tested for gonorrhea and chlamydia and results came back negative, no treatment was given. After about 10 days, the burning went away and everything felt completely normal. Four weeks later the pain returned. The burning seems more intense while sitting and is not particularly worse with urinating, although I do feel like I have to urinate frequently. Is it possibly NGU? Do symptoms disappear and flare up again with no treatment?