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This may be a simple pimple/staph infection however there is a possibility that it is a STD with ulcerated lesion. This will need examination by a doctor and appropriate antibiotics. The pus may need to be swabbed and you may also need urine sample testing.
Do not have intercourse until this is treated and completely cleared up. Depending on the cause, recent sexual partners may also need to be tested and treated too.
I would suggest that you go to urgent care or ER to have this examined.
A pimple is a small skin infection usually caused by a staph bacteria. The use of alcohol and a band aid may change the appearance of the pus. Pus is usually white cells, bacteria and the light brown may be due to blood from small damaged capillary.
Other possibility may be an infected sebaceus cyst, or very rarely, a syphilis lesion.
It needs to be examined as this is the only way to be sure of diagnosis.