Hello Andrea and welcome. I am not a doctor and I'm sure one will be along soon to offer you advice. To me is sounds like it is possibly eczema which the hydrocortisone cream (being a steroid) should help. You only want to apply a tiny amount of this. The ketoconazole is an anti-fungal so it looks like your doctor has covered all areas. Can I ask what country you are in? Just helps with offering advice. Eczema can take a few weeks to get under control and can return if treatment is stopped too early. I'm sorry I don't know anything about fungal infections.
I doubt your diet is causing it unless you have recently eaten/taken something new which could cause a reaction. Additionally if you have come into contact with something new it could also have caused it. Things could include animals, cleaning products, metals etc.
Eczema could also be caused by stress plus a number of other factors so if you thought the hydrocortisone cream was helping I would carry on using this as directed.
Hopefully better advice will be offered to you soon.