My german shepherd is 8 years old, and in great condition. He was just neutered 3 months ago. About a month ago, after a walk he threw up his food when we got home. Then a week later he threw up again after a walk. Then, today, he threw up his food again after a very long walk. He also got into the garbage today, and ate several used tampons. This has happened before though, and he was fine. I'm not sure if I should be worried or not or if I should take him to the vet.