Dog Started Peeing Inside?

My 4 yr old Westie is well house trained, but lately has been peeing indoors even when I'm at home. Circumstances have not changed at home in any way, but my dog has got allergies and his wee skin is really itchy. I had him to the vet's and he gave the dog steroids. He is so frustrated with the itching that when I touch him he's growling at me. He is not himself lately. He just lays around the house as if he has no energy and won't even play with his toys. Can any one help please?

Thanks.