Hi.
Thanks for your query.
Read and understood your history related to the redness and changes in the skin like yeast infection, used
lotrimin with some results, are with the same girlfriend for 9 years without any STD.
The most probable causes are:
Jock's itch, occurs due to hot and humid atmosphere, tight pants and so on.
There can be any sort of
dermatitis even due to retained sweat, soaps and sprays.
I would advise you the following:
Always send in a clear photographs which helps for on-the-spot diagnosis.
Clean the area with plain water 4 times a day, tap dry with cotton cloth.
Apply liquid
povidone iodine at least twice daily.
Consult a Dermatologist for proper diagnosis and treatment.
This can be in the form of an antibiotic, antihistamine,
steroids and oral anti-fungal preparations.
You will be fine.
Avoid hot and humid atmosphere.
Use loose clothes.
See if your sex-partner has similar problems, get her treated too.