Talk to Dermatologist on Jock Itch , Rash Or Eczema

i dont know its eczema or jock itch or rashes my groin skin like that blackish and woubd (zakhum) on groin i use hydrozyl and sudo cream but its give me temporary relief i take bath daily and change underwear daily . i wear cotton underwear breif so am i need to change underwear fabric because when i wear ubderwear for whole day mostly its happen i wear underwear in university whole day wear it if it happen dur to underwear so tell me best fabric and type for underwear which wear daily and for whole day