My husband keeps throwing up everything he eats and has diarreah and is lethargic what could be the problem?

Could be serious: Even without knowing the diagnosis - he is at risk of getting dehydrated and having serious complications as a result. Dehydration can be managed in the er quickly. Causes are many and include infection (probably first) - but should be evaluated urgently. Lethargy is usually a warning sign before other complications set in (due to electrolyte imbalance and water loss). Don't delay.