[Help] My dog won't stop throwing up.

I have a Great Dane/ Lab mix that was originally a shelter pup. He is almost two and a half years old and we've never had any health concerns with him until now. We haven't changed his diet at all. For the past about week and a half, my dog has been throwing up daily. It has just been clear liquid or grass that he eats outside. We haven't thought much about it until it started happening more often. Now it is happening multiple times a day and I have no idea what is going on with him. A vet visit will be happening soon. Any advice with this will help via /r/dogs http://ift.tt/2rYQSlJ