Since she's been having recurring episodes since 2010, has whipworms been ruled out? They don't show up on normal fecal tests, they need to do a fecal float test but it's still hard to spot, so treating for whipworms might be an idea...please relay this w/your vet. He/she shouldn't be annoyed, if that's the case, maybe you should find another more caring vet.
Dog Whipworm (Trichuris vulpis) Infestations in Dogs
Don't think pepcid is needed, as that's for acid. When Princess had her last colitis attack, she was prescribed amoxicillin & her poop firmed up on the 2nd dose...not sure if metronidazol is the best for colitis.
She also had subcutaneous fluids, as they lose a lot of moisture from going so frequently, they can get dehydrated fast. Lastly, I noticed you said dark blood. Colitis always produces bright red fresh blood, as it's inflammation of the lower intestine/colon. Dark blood is from the stomach or upper intestine...