This sound like urethritis although your tests are negative for any causative organisms.
The condition typically occurs due infections that may be or may not be related to your sexual activity. Most of cases however are due to infections with bacteria (Ecoli) that ascend through the urethral meatus (through intercourse or local contamination). Negative cultures do not exclude bacterial infection especially if tests have been done after starting antimicrobial treatment.
Urethritis can be diagnosed based on the presence of a mucopurulent or purulent urethral discharge; a urethral smear that demonstrates at least 5 leukocytes on microscopy field; and/or the miscopy finding of at least 10 white blood cells (WBCs) in sample from the first-voided urine sample or leukocyte esterase positive on dipstick test of a similar sample.
These symptoms could be also due to a urethritis that is caused by trauma or chemical irritants. There is itching and dysuria in the majority of cases. Avoiding the causing substance is the mainstay of prevention in addition to medications prescribed by your doctor.
Exclusion of STDs is essential and it is good that your doctor recommended it. So, I advise you to follow up with your doctor and to update him with your symptoms.
Please keep us updated.
This answer does not substitute for direct medical consultation.
Dr. Safaa Mahmoud.
MB BCh, MSc Internal Medicine. MD Medical Oncology.
PhD Experimental Medicine and Biochemical Science.