Hey! I have a stoma as well.
Which foods are you eating when the itchiness occurs?
How much water are you drinking?
Are you taking anything to bulk up your stool? Sometimes taking stuff to bulk up stool will help in itchiness.
Do you put anything around your stoma as a barrier? I use stoma paste or vaseline as a barrier around my stoma before I put bag on.
I definitely need the questions above answered so I can give a well thought out answer for you.