I second the oatmeal shampoo - but I would check with the vet & see given Oliver's specific condition which medicated shampoo he recommends.
Did he get an infection at the groomers? I would be speaking to them -- how sanitary are their conditions - or was he nicked & it got infected?? This needs to be addressed with them, and I think I would be sending them the vet bill.
Prayers for Sweet Oliver to