One possibility as you describe this is skin staph infection.
MRSA can act like this, which is a difficult staph to treat, sometimes, but treatable.
Fungal infection is the other likely possibility, and common in diabetes.
An anti-fungal cream would be needed if this is the case.
If staph bacteria, a cream called mupiricin.
That is the generic name. It is prescription.
This justifiably can go to A&E as it appears to be, or sounds like it is spreading.
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