Need advice ! Has anyone had a really itchy rash on their bump?

I started to get more stretch marks at bottom of my belly a couple of weeks ago and a rash has developed on it.

Doctor has given me a light steriod cream and emolliant cream which I have been using for a week and doesn't seem to be making a difference. Itch is torture (Not been scratching it) and keeps me up all night.

I'm at my whits end and was hoping to have a water birth but as heat irritates it, now looks pretty unlikely. ☹

Has anyone had this and got any tips?