It seems you are suffering from fungal infection
which is very common in scrotal and groin area because of local humidity,warmth and airless conditions which is very conducive for fungus growth and this specially happens in long standing uncontrolled diabetics.
Apply local anti fungal cream like CANDID
in night and dust locally with anti fungal powder in day time.
Wear loose cotton inner wears and change them daily.
Avoid using fragrant soaps.
Keep the area dry and take bath daily.
Keep your diabetes
in strict control.
You should be all right in next 4 weeks time.
May take oral anti fugal medicines,if symptoms are not releved by local application only.