Certain foods used to make my RB dog Sami throw up. She'd no sooner eat then it would be right back on the floor. Other foods, no trouble. She too was a grazer and loved to lay in the grass and nibble on it. Now that my Sasha is 12 years old, I've found that certain treats that she always used to get now make her throw up.

I agree that you need the blood work and a thorough check with the vet but you should also look at what your dog is eating.