Sweating and pain, with odour in left armpit

[Londoncitizen]

Can any doctor who specialises in treating sweat glad issues help?  I have had an issue for 4 years and still not been diagnosed.
When I sweat, I feel an intense twinge of pain under my arm, and then it breaks out into the most offensive odour, just on the left side, even though I have never had BO before. The GP can even feel a pea sized lump when they have a physical feel of it, which seems to come and go.
They prescibed me hibiscrub to wash with, but that only keeps the smell away for a few minutes, but it only returns when I sweat again.
At first they have prescribed me antibiotics in case of an internal bacterial infection, but that didn't cure anything. They then referred me to have an ultrasound in the breast clinic, they couldn't find anything wrong either.
The doctors then referred me to Dermatology, who I have seen several times, but they can't find any abnormalities on the ultrasound.
It is very distressing and I have to avoid social gatherings and cancel jobs because of embarrasment, it is ruining my whole life. I am tired of going to the doctor repeatedly, pestering them to do something, passed from pillar to post, still with no diagnosis. I keep suggesting it must be a blocked sweat gland but they say that any sweat gland issues should have been picked up by dermatology, which they haven't.