Welcome to HCM.
It may be either a hair folliculitis
or an intertrigo
doe to excessive sweating
or moisture of your thigh region.
For hair folliculitis, you have to take a course of antibiotic and to use an antiseptic soap.
For intertrigo, you have to cut short your walking habits, wearing cotton clothes, application of steroid creams will help you.
You better have a consultation with a Dermatologist
.He/she will help you in this regard.
Get well soon.