Puppy won’t eat, low energy, vomited water-like stuff a few days ago, today yellow fluid.

Vomiting, low energy, and poor appetite have many causes; if the dog is in poor shape, take it to the hospital promptly. It may be acute gastritis from long-term poor diet or spoiled food, causing retching and vomiting – give cimetidine tablets to stop vomiting, withhold food and water for 6-8 hours, then give probiotics and Essuda antibiotics if vomiting eases.

Vomiting may also come from swallowing a foreign body blocking the gut – if frequent, see a vet. Internal parasites cause similar signs; deworm after vomiting settles. Finally, an unvaccinated dog may have distemper or parvovirus, with lethargy, appetite loss, fever, and diarrhea – seek hospital care.