Is there any history of diabetes?
Redness on the shin or anterior part of the leg may be due to following reasons-
2.2.Diabetic rash (if you have diabetes)
If there is increased local temperature & raash is tender then it is due to cellulits.
If this is not tender & it is itchy then it may be due to ring worm or dermatitis.
You should consult to your dermatologist & get yourself checked for diabetes & thyroid function tests.
Hope this will help you.