I am sorry to hear your dog isn't feeling well. There are many reasons why a dog would develop digestive issues. These range from having eaten something odd that upset them to liver disorder, to bowel obstructions, to having ingested poisons. So, obviously with this many and more possibilities, it would be hard to tell you what is going on exactly. I can help you to decide when to bring the dog to the vet and with some home treatments for digestive upset.
I would take the dog into the vet if he is refusing to eat anything (even special tidbits), is unable to keep anything down, is very lethargic, seems painful in the abdomen, or has vomiting/diarrhea for more than 3 days. If your dog begins displaying any of these signs I would get to the vet.
For home treatment of digestive upset, the most common recommendation is to fast the dog for 12 - 24 hours. You can offer fresh water, ice cubes, and pedialyte. This is to give their system a chance to settle down. Then start them on a bland diet of boiled chicken or hamburg and rice (3/4 rice). Feed this for several days then transition back to normal diet. There are also some over the counter meds you can use in dogs. I have found immodium to be very helpful for diarrhea. A 50lb dog would get the normal 2 mg tablet - you can give every 8- 12 hours. It usually only takes one or two doses. If it doesn't work in two doses, I would bring to the vet. (I do always recommend checking with your vet prior to giving any medications) Here is a link to more informatioin regarding over the counter medications.
I hope that this helps. If you need more information, just reply to your question.
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