This is a great question. It is very important that you make an appointment with your primary care doctor
soon to discuss your rash and have a full history and physical. Although it is difficult to know the cause of your rash without seeing it, there are a few possibilities for what it could be. The first is, as you mentioned, a fungal infection, likely caused by yeast or tinea (ringworm) from the dampness and lack of oxygen from the compression shorts. This would be treated by an anti-fungal cream. Another possibility is that you have an abscess
, or infection under the skin. This would be more likely if the area feels warm and it is painful to touch. This would be treated by antibiotics and sometimes an incision and drainage. It is also possible that you have a cyst, or collection of fluid under the skin. These can be monitored as they are benign, but they can be removed via a simple outpatient procedure if they are uncomfortable or if they get infected. Again, as there are multiple causes for rashes it is important that you seek care with your doctor to get a correct diagnosis and appropriate treatment.