My Almost 25-year Old Son Has Been Nauseous And Throwing

My almost 25-year old son has been nauseous and throwing up (off and on) for several days. He seems to keep some food down but then vomits at some point within several hours. Has been trying to stay hydrated; no fever; doesn't feel tender or have any real discomfort other than the vomiting. Concerned that this has lingered for more than a day or two. thank you.