Sick dog:-(?

My dog all of a sudden got sick this morning. She was fine first thing but a while later she threw up her food, then every once in a while, she'd throw up like a yellowish thick liquid. Seems a bit weAk, I took her outside and she still fetches toys and runs normal. She has not had diarrhia. She is pretty up to date on her shotS. I have to take her soon to get her 2nd set. Tomorrow is Easter so I will have to go monday to the vet. Any Idea??? She eats purina one..large breed.....could she be getting too much nutrients from the food...She is a boxer/bull mastiff mix..thanks so much, dog lovers know how I feel....nervous...