Severe left-sided stomach pain radiating to your left shoulder after consuming food or water can indicate irritation of the diaphragm, often related to conditions like gastritis, a stomach ulcer, or severe acid reflux. Because these symptoms require proper evaluation, you should consult a doctor before starting any treatment. A physician may recommend tests like an endoscopy. For temporary relief of possible acid irritation, generic over-the-counter medications like famotidine or omeprazole may be suggested. However, because the pain is severe, please seek professional medical care promptly to get an accurate diagnosis and a safe, targeted treatment plan.