I have a burning sensation and pain at the head of my penis. no problem in urination. pain when i ejaculated and afterwards. no marks visible ?

Infection: This may be a sign of a urine infection. You need to see a doctor for a urine culture to see if this is an infection that needs to be treated.

Prostatitis: The most likely cause of the symptoms you describe, particularly in the absence of other urinary symptoms, is prostatitis. You should see a physician for urinalysis and digital rectal examination. Urinalysis and urine culture may be normal with prostatitis however.