What Causes Wetness Between The Two Cheeks?

Every now and then wetness comes between my two cheeks at the bottm od my rear end. The wetness is clear and when I wipe it with tissues i t then goes away I have put some Desiten for childrens diaper rash on it and it does help but then all of a sudden out of know where it come back Naturally from wiping it it then becomes sore and irritated. Is it some kind of fungus. I don't have any pain but it is anoying.