At the moment I'm using Lotrimin Anti-fungal cream, which seems to help alleviate symptoms, and
would hypothetically treat jock itch
if I have it. What makes me 99% sure its yeast is that when I do use topical creams like Ketaconzole, the symptoms disappear entirely within a few days, and only return when treatment stops.
In terms of diet, from what I've read avoiding sugars and excessively 'flour' based foods is best.