About twice a month i get a very itchy rash on the inside of my foot. what could this be?

Fungus or allergy: The two most common reason would be a fungus or an allergy. Luckily, there is a product that would treat both. Ask your doctor for a trial of lotrisone (clotrimazole and betamethasone)...Using this periodically may solve the problem!

Need eval to know: This rash would likely need to be examined and more history obtained to be able to provide you with useful input about the diagnosis or possible treatment.