Although perspiration is basically odorless, it can take on an unpleasant smell when it comes into contact with bacteria on your skin. Most often, it's the bacterial breakdown of apocrine sweat that causes a strong odor.
The other reason could be a fungal infection of the skin. To check whether it is a fungal infection or not, you can get a KOH examination of the skin scrapings and fungal culture done.
It is very difficult to precisely confirm a diagnosis without examination and investigations and the answer is based on the medical information provided. For exact diagnosis, you are requested to consult your doctor. I sincerely hope that helps. Take care and please do keep me posted on how you are doing.
Socks: wear merino wool socks or other very good drywicking socks (check google. it's pricier but worth investment). also bamboo socks have good reputation and are cheaper.
Shoes: geox, or make sure it’s breathable shoes like leather
Insoles: Cedar wooden soles!! this is a must!
Then ask yourself if this is a bacterial overgrowth, fungus or sweat problem. Best to always check with a dermatologist!! Go to one!!!
Bacterial overgrowth: You can check if fucidin lotion (note it’s a medicine, don’t overuse) can help you. Sometimes anti acne lotion can help such as clindamycine or benzac 10% . The bacterias causing zits can sometimes be same bacetrias causing smell. Do please check a dermatologist before proceeding with these lotions. You can apply 3 times in day for a month, and changing socks everytime.
Fungus: check for topical antifungus like clotrimazole . Again, check with dermatologist.
Sweat: Apply strong anti perpirant (15–20% aluminium chloride), if that doesn't work check into buying an iontophoresis machine and combining with glycopyronium bromide medicine, if that doesn't help there's a surgery only if you have plantar hyperhidrosis (it's called lumbar sympathetomy)
ALWAYS WASH FEET IN MORNING AND NIGHT WITH HIBISCRUB (it has chlorexhidine gluconate 4 %. it's bactericide for hours)