Eczema/atopic dermatitis question ?

Hello, I've been fighting this rash for months now and finally, my 4th doc visit have gotten a realistic answer to my problem. My doc started me on steroid cream, benadryl and light treatment (ill start that monday) does anybody know how long it should take for the itching to ease up now that im on the right meds for this?? The bendaryl is a grear sleeping life saver, I didn't wake up once in the night scratching my arms, but I think its wore off now and im itchy again. Not nearly as bad, but still frustrating. Thanks all! :)