Thanks for your query.Based on the facts that you have posted it appears that you have Chronic Ballano Posthatitis. (Mucocutaneous Genital Candidiasis
As this is very common in diabetic individuals Please get your blood sugar levels done to rule out Diabetes
Take anti fungal medications orally along with topical anti fungal gel for local application.
Get the prescription of these drugs from your family Physician .
If you have difficulty in retraction of foreskin over glans
consult qualified Urologist
for clinical examination .
You may need to get circumcised under local anaesthesia.This will solve your problem permanently.