1.5 year golden behaving oddly after a heat rash at the boarding

[NDhanawade]

my golden retriever is 1.5 years old. He was at boarding for a weekend and came back with a very bad heat rash on his neck and upper chest. We took him to the vet immediately where his hair was shaved off and he is under medication. This is day 3 and the wound caused by the rash appears to be healing forming scabs and all. We clean it thrice a day as advised by the vet. He had not pooped since the time we got back and is resistant towards doing anything at all. Just keeps lying on a sofa and is not interested in food, toys or even outdoors. This is very odd since he is a golden and has been extremely active. Due to this odd behavior, we took him to the vet again yesterday. They took an xray and did blood work. We were told there is nothing medically wrong with him. While he came to the backyard today and was smelling a bit, he pooped without realising. He was shocked and went running inside. We then forcefully set out to take him for a walk - and he just pooped while walking on the sidewalk. He was scared and didnt know what was wrong. I am really really worried. He is not the dog I know and want to go into hiding his neck all the time. Not sure if he is feeling weird or ashamed with the hair gone - he is giving the same look he would when scolded on doing something wrong. He is behaving so indifferently with both me and my husband. Please - need some advice on what can we do to get him back to his normal self? He seems to have withdrawn from us.