Hello and thanks for your query. I shall make an effort to provide you with good professional recommendations specific to your questions. It is always difficult to diagnose a rash on any part of body without examination or without at least picture of it. Often a man becomes concerned if a small spot or bump appears on his penis. There are many causes of a small red spot, Excess pressure, tension or overuse and injury. Rashes are often accompanied by itching, and both can be caused by irritation, an allergic reaction to a detergent or soap used in the groin, or infection by a sexually transmitted or non-sexually transmitted organism. As you have mentioned antibiotics have not been helpful, It can be a yeast infection which requires prolonged treatment, but it is difficult to diagnose without examination. So i advice you to see doctor for examination and exact diagnosis. Yet again, I duly appreciate your query to me, I do hope that have found something useful to help you and I shall be glad to answer any further apprehensions. Sincerely,