Has he been tested for laptosporosis?? Whats his BUN and creat
I am so sorry your boy is so unwell. If the vet has said he has Tick fever and he has done blood-work and testing, then I think you have to go with that diagnosis.
Do you know what shot he was given? An antibiotic? And did the vet also give you antibiotics to give him at home?
In which case, you will have to be a little bit patient, and allow the medicine to start to do its work. Tick fever is quite serious, and he will not feel too good until the drugs kick in. Let him rest and heal. I hope his appetite will come back very soon.
In the meantime do whatever you can to stop him getting dehydrated. If he won't drink water (many dogs won't if they are not moving much, not feeling good and not eating) -then try some honey dissolved in water (and cooled) or some stock like chicken stock in water. But not too slaty as this will make dehydration worse. The best meat stock for dogs is water in which unsalted meat and vegetables have cooked. He might even be tempted by some of the home cooked food?
An unwell dog is more likely to feel interested in some home cooked meat and vegetable stew, than dry kibble!
I do hope he picks up a little bit very soon.
If it is Lyme disease, then the antibiotics are strong and even that can cause appetite loss sometimes. Also the course of treatment I believe, is for a longer time that usual. Ask your vet about it.