My daughter has a rash that comes and go for about 6 months i took her to her pcp 4 times?

she gave her creams that do not work i took her to the dermatologist and he said is just a diaper rash but i know that diaper rash looked on her before and this is not diaper rash she no longer warediaperr any suggestion would really help i am tire of dealing with doctors who do not help please any suggestion is welcome.