In order to receive a formal evaluation and possible treatment if necessary, I recommend that you see a healthcare professional for your symptoms. Painful, swollen sores on the penis can have multiple causes. Testing for sexually transmitted diseases in males involves testing for syphilis, chlamydia and gonorrhea, however, these cause purulent discharge from the urethra, but are not typically associated with penile sores. Genital herpes can cause isolated, non-itchy, painful, swollen sores of the penis. There is no test for herpes unless sores are present, in which case the diagnosis is made by history, physical exam and culture of the lesion for the herpes virus. The more sexual partners one has, the higher the risk of developing this condition. Other causes of open sores on the penis may include trauma, often in the form of repetitive injury
due to frequent masturbation or sexual activity. Sometimes bacterial infections of the penis may cause an open sore, and may be associated with swollen inguinal lymph nodes. Mononucleosis generally does not cause sores of the penis that you describe. If the lesion has not improved, it is important that you see a doctor
in order to undergo the appropriate testing and treatment needed, if any.