The most obvious causes for your dog's symptoms include:Giardia, Pancreatitis, HGE, IBD, Parvo, and stress colitis. Another possibility is a GI foreign body (The GI foreign body would require a barium study and possibly surgical removal of the object). There are snap tests for giardia, pancreatitis and parvovirus that can be performed in-house immediately.
These diseases, except a GI foreign body require symptomatic therapy at the vet's office. They usually require IV or SC fluid therapy, antibiotics, H2 blocker, an anti-emetic (anti-nausea medication), Sucralfate (band-aid for the bleeding in the GI), and others, and fasting (to rest the gut) for a couple of days. Fasting is OK for dogs, since they do not get fatty liver disease (hepatic lipidosis) in the way cats do. Abdominal X-Rays and blood work is necessary to monitor the progress of the therapy.
These disease can be very serious without therapy and may rarely require surgery if the intestines telescope into one another. IBD will require a hypoallergenic food once your dog is well enough to eat.
Please let us know how your dog does!
Thank you for the input on the bowel issues. My poor little dog is still sick. After another trip to the vet, he took her off Doxyciline but kept her on the Metrozindale. She was good for 3 days, although vomiting up some of her food. Then she had lots of bloody diarrhea, vomitted blood. I took her to the emergency vet. After an ultrasound, she had enlarged spleen and lymph nodes with no fever. The vet is leaning towards IBD or worst case Lymphoma. The needle biospy was inconclusive. He put her on more Metrozindale, Prednisone and something for her gut. But then she started to bleed from the tip of the ears. The vet said it was vasculitis and he tested her for tick titers. But the tick titers have come back negative. What could possibly be wrong with this poor dog? What other diagnostics should be run?
Update: She now has red sores at the corner of her eyes. And a lump above her eyelid. Although the vet thinks this might possibly be an immune response to the high dose of prednisone. He wants to see her in again, to check her lymphs and spleen.