I sort of understand the middle of nowhere thing. A friend of mine recently just moved, and the vet in her area does routine shots, but will not go on emergency calls, because they say its "too far". She doesnt own a truck and trailer. She's having a very hard time trying to find a vet that will come, even if they are 2+ hours away, and most it seems just don't want to do it. She's trying to find someone now, before an emergency occurs, and she said she's having a really hard time.
For my mare, this started with lack of appetite on friday, fever on saturday, sunday. My vet came out on monday. Blood work came back tuesday, and we started antibiotics on wednesday. So she spent almost 6 days like this with my nursing her, before we were able to pinpoint the issue and start treatment.
Im not going to badger you about the vet. Keep trying to find one, or a truck. In the meantime, do the best you can. You need to get some blood work done asap. Does this horse have all of its vaccinations? Flu/rhino, tetanus, etc? Could be a virus, or a flu, or inflammation due to parasite damage. Then again could be none of those things... but ill do the best I can to help you.
Remember, Im not a vet, so take my advice at your own risk. If this was me, this is what I would do. #1 contact a vet, keep calling, and keep trying to find a vehicle to haul you somewhere. #2 keep in contact with your current vet, keep them updated on the situation and follow their instructions. #3 check their vitals often, heart rate/temp/manure/gut noises/gum color, etc. Going on the idea that this is some sort of colic-related situation. Rmember, colic covers a wide range of things...
No more grain for now, if theres any inflammation, grain will make it worse. My vet said I could offer hay and water. If they are uninterested in water, you can soak alfalfa cubes in a bucket of water and offer that, to try to avoid dehydration. Before you give another dose of banamine, check the temp to see if its going up as the banamine wears off. If theres an infection, the banamine will keep it down for a short time, but it will probably go back up, as you get closer to 8 hours.
If a fever develops: You can hose them off with cold water, I did this once an hour for 14 hours actually. And then every other hour through the night. Laying down quietly is ok, rolling and thrashing around isnt. YOu already know that and are addressing that part.
My mare had bloodwork, and even so, her white blood cell count WASNT up! My vet said it was probably a localized infection. We treated her with Bactrim anyways, and I saw an immediate improvement after 12 hours. Its been a week now since the Bactrim was started and she's back to normal, but I had 4-5 really bad days with her!
Im sorry that you are having such a hard time finding a vet. Its super important that you have him seen before monday!