Is it common for a fungus infection (ringwarm) to cause your groin lymph nodes to swell? Went to the doctor he prescribed me a steroid (predisone)

Fungous infection. If the fungous infection has been on your feet for a long time, it can spread to the lymph nodes in your groin. You probably would need an oral ringworm medication if it is a ringworm. For other infections in the groin, like a bacterial infection, an antibiotic would be indicated. A dermatologist might be the one to consult with.