How to get rid of a unknown rash?

I have had a rash for about 3 months now. I have had 3 tubes of the scabies medication cream. 6 medrol dose packs & still not better. I have used hydrocortizone cream. & eucerin lotion also. It itches & burns…it’s on my back stomach, sti
Stomach, hands, thighs, bends of my knees & arms. I just want relief from scatching & itching.