On 24 aug, had a unprotected oral from csw, ejaculate on mouth. On 4 of sept, started to feel uncomfortable on penis, pelvis, and perineum. I oftenly masturbate (once a day since the encounter). Feelng pain on perineum area, back of testicle and side of penis. Urge of unfinished urination. Since then i masturbate once every 3 days. Symptoms worsen only after ejaculation. No discharge at all. Went to urologist, did an usg, doctor suspect of prostatitis (i had it earlier last year), or muscle problem. Doctor gave me fosfomycin 3g. However, Could this be a symptom of an STD? Does urine test helps? Does the fosfomycin helps for stds? Should i wait to have sex with my partner?

Thankyou

Oral sex is not entirely risk free, but it's very low risk for all STDs and zero risk for some. STDs do not cause "uncomfortable" sensations of the pelvis, lower abdomen, testicles, etc, and with neither discharge nor painful urination in the 2+ weeks since the event, you can be very sure you acquired no STD. STDs also do not cause urgent urination:  that is a symptom originating in the bladder, not the urethra. As you apparently have experienced previously, these symptoms are typical for prostatitis, and for the male chronic pelvic pain syndrome (CPPS) (which is perhaps what has been diagnosed in the past when you were told about a "muscle problem").

Assuming your doctor considered prostatitis a possibility, it was reasonable for you to be treated with fosfomycin. It won't help if you have CPPS, but it's certainly worth a try. It will have no effect on any STD. Presumably you have been tested for common STDs, in particular gonorrhea and chlamydia. If not, it would be reasonable to do so, to be on the safe side. But even if a test is positive, it will not explain your symptoms. At this point, I see no reason to not have sex with your regular partner -- especially if you have had negative STD test results.

I hope these comments are helpful. Let me know if anything isn't clear.

HHH, MD