mr sunflower has exactly this!
It came from our washing machine not rinisng the poweder out properly.
anyways we have tried EVERYTHING but the best thing that is keeping it under control is,
im sorry i cannot remember what exactly its called but its a small tube yellow in colour (packaging) something like lancester, lancter.
Also some aquenous (??) cream to moisurise.
Had out first undisturbed night last night without him itching or moaning!
make sure you dont use anything perfumed in bath or shower.
all the best