Thanks for the query.
You seem to have developed either a friction blister
or podo pompholyx
So either it is due to skin friction from your footwear.
Or it can be an eczematous skin condition.
You might need treatment with topical steroids
Take oral antihistamines for the itching.
Wear soft canvas footwear.
See a local dermatologist
if the lesions persist or increase.
Hope it helps
Dr Geetika Paul