You say you " caught " jock itch " - there must be something in the routine you have that has caused this. I am thinking specifically about the kind of routine you have with your gym visits, the amount of showers (or none perhaps) you have each day, and, whether you change into fresh underwear when you excercise, then, when you are getting dressed again?
There is something that has gotten to be part of your routine that is causing an extreme dermatological reaction.
My first approach would be to stop putting ANY chemicals - whether medicinal, shower gel, hair shampoo and so on from getting anywhere near your groin region! Rinse thoroughly away soaps etc you use on other areas of the body to maintain hygiene in those areas of your body if you need to.
THEN, in other areas of your life, you need to think what other chemicals that are a regular part of your life that have become part of this extreme reaction. This can be the likes of washing powder residue on the clothes, and particularly the underwear you regularly use, as well as the dedicated sports wear you put on to do ALL the regular exercising you do. If you are sexually active, for instance, are condoms a regular part of your weekly way of life. Condoms these days are full of all kinds of chemicals that can have an extreme dermatological reaction. I am not suggesting the issue you have is caused bu any one single item. What many people are likely to have is a toxic mixture going on, and, your skin in that area is basically telling you that it has had enough of this toxicity.
In these kinds of circumstance you can rule out one thing at a time: washing powder, shower gel, and so on. Doing this may take too long and may leave you with the terrible itching for too long.
Perhaps you could get a referral to a dermatologist, if this is possible, as, what the doc has tried has not been successful for you! In the mean time, I would let your watchword be - if it is not natural, water only - don't let it get anywhere near your crotch area. For your clothes - try getting natural soap flakes that you can use in a washing machine: make sure all your underwear and gym/sports clothing are washed this way. Se if you can have a positive impact by doing these changes for yourself - if you cannot cure this yourself, you must get to see a dermatologist to puzzle out what it is you have going on.
Good Luck - W.D.