hi gemma my 7 week old ram lamb went off milk and concentrate and was doing the back stretching thing you mentioned. Back stretching is usually a sign of abdominal pain, poss kidneys. So i was concerned wit my lad and diagnosed abomasal bloat (as oppsed to rumenal bloat found in adults, and sadly harder to deal with) If any lamb is off food and or stretching and or tooth grinding i would assume abomasal bloat ie gas in the lower belly. it can not be cured by tube via the mouth, or bicarb by mouth- the only method i have had success with - on advice from vet (recently in a 7 week lamb and previously in a 2 year pygmy goat) is injectable antibiotics to kill the gut flora and stop fermentation and gas production, then re establish gut flora once animal is starting to eat again. Pain relief is good and i also tried an ant acid prep i use for my own gut pains (zantac- known as ranatidine which vet says is oft prescribed to dogs with stomach ulcers. i think pain relief is more helpful than historical animal meds give credit to.