Fixed drug eruption
The lesion that you have developed is most likely that of a fixed drug eruption . Now this basically a type of allergic skin reaction which develops on intake of a drug to which our body is sensitive.
The lesions in this case are round or oval and reddish or purplish in color. Male genitalia is a very common site of development of these lesions.
Although such a sensitivity reaction to drugs commonly occurs after intake of pain killers and antibiotics but in your case, you cannot recall the intake of any such drugs before the development of this lesion. Even sometimes the preservatives and coloring agents added to various foodstuffs can lead to development of these lesions which seems to be the possibility in your case. Also do try to recall if you took any medicin in the form of pain killers or cough syrups prior to development of lesion.
Now as far as management of the same is concerned, it is important that you see a nearby dermatologist
so that , if required, a drug assay can be done to look for any offending drug which can be avoided in future.
At present, you need to maintain a proper local hygiene by effective cleaning of the area twice a fly with lukewarm saline water.
After this, you can apply a topical antibiotic
cream like mupirocin
or fusidic acid
to the lesion twice a day. The lesion is seemingly infected with pus discharge so you should avoid touching it too much.
In addition, you can take some oral antihistamines tablets like benadryl along to bring down the allergic reaction
Since the lesion is infected, I would have given a course of oral antibiotics
500 mg once a day for five days to my patients as well. You can discuss this with your treating doctor.
Do not apply any other oil or cream to the affected area.
Also you can rest assured that this is not a std. It is just an allergic reaction which has persisted so long probably because of inadequate treatment.
Hope it help
Please ask if you need any further clarifications
Dr Geetika Paul