Rash on inner thighs can be due to synthetic clothes, infection or insect bite. If the rash is not infected then use hydrocortisone cream twice a day for few days and take anti allergy medicines. In case of infected rash apply topical antibiotic. It will be better to visit a doctor for proper diagnosis and treatment.
Try neosporin ointment then put caldesene powder over it [this powder is in a pink plastic bottle on the baby aisle at walgreens] this would help the rash/