4 Year old german Sheppard wont stop throwing up?

Take him to the vet asap! The same thing happened to my dog last year... She was vomiting at least once per hour, even when I didn't feed her anything. I found out that she had an obstruction and the vet had to do surgery to remove a foot of her intestines. Has he been eating gr alot lately? Sometimes they do this when they have a tummy ache. The yellow stuff you see is bile and that's not good.... Could be something like pancreatitis, It's usually due to feeding fatty foods or too much people food... I found this out the hard way, my dog almost died from that but thankfully she pulled through and I kept her on a strict diet after. If he's vomiting that often, it's definately serious and you need to get him to a vet now!