Acid reflux meds treat the symptoms without trying to solve the problem and sometimes that makes the problem worse. Your dog should be weaned off the prilosec over the course of a few days, not stopped abruptly. My dog had to be feed small meals a often as I could for a while. The thing that seemed to help the most was 1/2 teaspoon of apple cider vinegar per cup of food and soaking the food. It seems counter-intuitive to add more acid to the dogs stomach when they appear to have an acid overload problem, but really the opposite is at work. High grain diets alter the normal pH of the stomach and the sphincter muscle at the top of the stomach is acid sensitive so isn’t closing all the way. My dog was having problems with this as a 8- 10 week old pup, when we changed his diet to high protein and started adding the vinegar, he ceased to have problems with vomiting anymore, and hasn’t since. He is now 14 months old.
