Labrador Vomiting

I have a 3 year old yellow Lab named Cowboy, for the last 4-5 days he has been vomiting whenever he is resting after play. He doesnt throw up any food, just basically dry heaving. I thought at first that it was due to him drinking too much water after, but even when we dont let him drink, he does the same. He seems to be fine after he calms down. Any suggestions? Thank you!