My dog started shaking his head and gagging and then he vomited white milky stringy stuff. It has started and stopped several times now. He is scared . Can anyone help?

if you are a client at this vet office then you can call them and do an emergency visit. Dr Taylor is wonderful. You just have to be an established client. Also cashua veterinary clinic has an emergency after-hours as well if you're an established client. basically you can call up there and tell the answering service what the issue is and dr. Taylor can call you back and see if the pet needs to be brought in. If not there is an emergency vet clinic in Columbia.

Did he eat something poisonous ? Is he choking ?

No he's not choking he's drinking water and until he starts shaking his head he just seems normal,but scared