Hi
This does sound like CFS but other tests should be done to rule out other conditions but with no health coverage i dont know how your do that i am in the UK.
With CFS diet is important and maybe keeping a diary of what you eat compared to what sx you get maybe helpfull as you mentioned you get weak and shaky after eating.
Its important with CFS to get a balance of pacing resting and relaxation, do a little at a time when you feel well but dont push to much or your end up in a flare.
walking is a good exercise but again build up very slowly also hydrothreapy (gentle exercises in warm water with a qualified physio) is very helpful as your body is supported i have fibromyalgia which they say is a simular if not the same disease but manifested in a different way.
You are doing all the right things with your diet.
Did the dr's not give you any idea what this could be or do any tests?
sorry i cant be of more help.