I had a 6 year old (45 pound) Border Collie who had all the same symptoms (except the bloating) and I immediately took him to the vet who diagnosed him as having a Hernia. How he got a Hernia I have no clue. My dog had surgery and recovered very nicely. The surgery though, was rather expensive but well worth it as my dog lived almost another seven years. This may not be the case with your dog, but you must have your Vet check him out.
