Hi lovell
I am not an expert on dogs, but I do have a Westie and also had one that passed away 5 years ago.
They are prone to rashes, my present Westie does not have this, but my last one did.
He was treated by the Vet with steroids to start with and also special shampoo.
After that, the Vet prescibed Piriton which is an antihistamine. IT did help the rash and also the itching.
It may be an idea to try just a soft collar and lead on him.
Take him to the Vet anyway as they will prescribe the proper medication.
Hope he is better soon.