This could be a heat rash
...or a rash
from continuous rubbing ( from your legs rubbing together as you walk.)
Bad clothing...some contain latex, chemicals, etc that your body is protesting to...can also include detergents etc.
Sweat rash is also possible, as are insect bites.
Fungal infection/jock itch, soaps, shingles, STDs, ( syphilis, herpes, or warts; cause rashes on the inner thighs in both women and men.