Undetermined illness, possible Prostatitis?

Patient: About 6 months ago I began getting symptoms that included a tingling at the tip of the penis, some groin aching (nothing severe), and a feeling of something wanting to be expelled from my penis but nothing coming out. At one point there was discomfort at the tip as well but that came and went and has not returned. Recently, the symptoms have returned with what seems to be a twitching or pulsating of the perineum. Discomfort, lower back pain, and what seems to be a tiny bit of clear, sticky liquid comes out of the penis (very small amount and very rarely, maybe 3-5 times ever) occurs along with the pulsating perineum. I have underwent STD tests, as well as urinalysis tests and everything has come back negative. My doctor seems to think it is mental, but I don’t see how this is possible. I have read maybe prostatitis could be a candidate with these symptoms, but I am far from an expert. Any thoughts?