If you visit the dermatologist, and s/he diagnoses a fungal infection, you may be given oral medicines as well as a cream to put on your feet. Hygiene is very important for preventing recurrence: washing socks in hot water, washing shoes if possible with an anti-disinfectant, or at least laying them in the sun as open as possible, as often as possible, and washing your feet then drying them after workouts, after getting home, and before bed. You can also try drops of oil of oregano diluted 1:2 in olive oil. Place between the toes, if the skin is not cracked. This oil is very potent for fungal infections on the feet and toenails. Lastly, you can make a strong tea of Neem bark (neemtreefarms.com) and soak your feet in the tea for 5-10 minutes each night for 5 days. Neem is a potent antifungal and cleanser and has been used for 5000 years in India as a antimicrobial before the antibiotic age. Good luck...!