Hello again. It appears you went offline without seeing my request for more information. Because I don't want you to wait any longer, I'm going to go ahead and answer as best I can without knowing those things. Your dog's symptoms do indicate an upset stomach. With excessive acid production or acid reflux, we often , but not always, do see vomiting of yellow bile. There are some things you can try.
More frequent feeding often solves the problem. If you feed him only once or twice a day, divide the food into several smaller meals. If the upset occurs at night or before breakfast in the morning, it would be most important to give him a small, starchy meal just before you go to bed. Well-cooked rice (instant is fine) with a little plain yogurt (not sweetened with sugar or artificially) is a good choice. If you get up in the night for a drink of water or to use the bathroom, give your dog a snack of a biscuit, a saltine cracker, or several pieces of kibble. I keep biscuits in a plastic container on the nightstand for this purpose. Sometimes a bit of food in the stomach is all it takes to help this problem. If the stomach upset occurs in the daytime, give small snacks throughout the day so there is always a tiny bit of food in his stomach.
You can also give your dog a 10mg. tablet of Pepcid AC at bedtime, along with that last meal of the day.
The above steps are most important, but you can also switch to a food for sensitive stomachs, and try digestive enzymes, such as Prozyme or N-zymes. They are available from vets and in some pet stores.
If these measures don't solve the problem, it would be a good idea to see your vet. Your dog may have an ulcer or other problem that will require prescription medication.
One of my own dogs has this same problem, and she used to be sick almost every night. Since making these changes, it only happens once every couple of months. I hope you get similar results. If you have further questions, just let me know.
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