Is it on your rude bits or on your legs? If its your legs it could possibly be eczema,(buy hydroquartisone cream and soap free wash) or a rash from your legs rubbing together/salt water ETC. (just buy some 3B from the pharmacy for that, it should clear up) If you've got smelly discharge as well it could be thrush. That's a yeast infection, and can be treated with Canestan Duo, (Tablet and cream from the pharmacy) Otherwise it could be an STD. If you've got pain or a fever go to the doctors.
Good luck