Dog keeps vomiting

For context: my dog started throwing up on saturday. He threw up 3 times the first was a bit grey with some grass in it. On sunday he threw up twice. Today, tuesday, he threw up again this time it looked a bit yellow. I plan to take him to Mexicali as it is much more affordable, but i would like a second opinion as i wouldnt be able to take him until this friday. Is there medicine i can give him? Should i be concerned? He doesnt seem lethargic he shows signs hes interested to eat, but holds off sometimes