I've had the same problem for way more than three years and it was terrible no matter how much I bath it was never enough...Once I started taking probotics a few years ago I immediately stop because seem like the odor intensified...Recently started taking it again and weathered the strong smelling odor and now Im only having good days..The higher the probotic number the better but this work for me hope it works for you.
Some people complain of an odor that comes from a leak at their umbilicus where at birth it did not close completely and there is a little infected or bowel smelling liquid escaping. I don't know if that's what you mean since you say it's related to sweating.
Get tested for Celiac disease.
Avoid eating dairy if you have not tried that.
Take a prebiotic like Align.
Consider your soap. Maybe you are reacting to it. Have you tried changing it.
Have you tried baby powder (talc not corn starch type).
Could it actually be foot odor? You can start soaking your feet once a day in a solution of diluted white vinegar or you could urinate on your feet in the shower. Honest, that's a cure for foot odor.
Have you tried "baby wipes."
Are you using antiperspirant, not just deodorant.