It seems that you may be having frictional dermatitis
,caused by friction of thighs due to big thighs during walking.You should do exercise to reduce the fatty thighs. Take antihistaminics like levocetirizine
and apply mild steroid cream on the lesions. If needed, you may take steroids
in tappering dose. Avoid soap bath.
If there is secondary infection, take antibiotics.
You consult dermatologist
and have blood tests to rule out DM and other internal diseases.
I hope you got my answer.
Dr. Ilyas Patel MD