Feeding a Sick Lethargic Dog?

I have a 6.5lb Pomeranian who abruptly woke up on April 8th looking sick and symptoms manifested quickly. She is only 6 yrs old very high strung and full of anxiety and has separation anxiety. Now she is lethargic, doesn't want to play at all, sleeps almost all day, she squints her eyes especially the right one and often cocks her head to the right, she jumps on furniture, but is apprehensive about moving from one piece of furniture to the next and doesn't like to jump down, and she isn't very responsive when you call her. The only time she gets excited is when she thinks someone is coming home and she starts barking or when it is time to eat people food cuz she will not eat her hard Nutro dog food up to now.

Right now we've seen two vets and have taken her to a neurologist who gave her Gabapentin .5 2x daily and recommended an MRI of her brain and a spinal tap which we can't afford and he understands. The specialist says there is no guarantee if we do it that he will find something, so right now were using trial and error. The other vet prescribed Doxycycline for 2 weeks to see if it will treat whats going on if it is in the brain or spinal chord fluid. If it doesn't work then we will try steroids next.

Has anyone ever had a small dog with these symptoms? Next, I am needing help in knowing how much food and what kind of food to feed my Pom for her size. Currently, I have been feeding her 2x daily either tuna fish, boiled chicken, 1 egg with cheese, coconut oil, and green beans. I've been giving her approximately 1 oz of protein. She used to get 1/2 cup daily of venison Nutro dog food recommended by a vet. Thanks.