Scout is definitely not healthy right now so lets break some of this down...
The history you describe sets up the possibility for several things: still a bacterial inbalance, parasite infection, IBD (which is immune related), or allergy.
First, keep in mind that an allergy can arise at any time and to any substance - even one that the dog has been eating his whole life without incident. So there is no assumption to me made based on historic diet.
You describe lack of appetite - this is key! To truly test appetite, offer a biologically appropriate food for a dog that would be instinctively attractive - not RICE
but meat! Offer this as as a meal and see if fresh food is of interest. This will tell you if there is an issue with the kibble...or truly a lack of appetite.
If lack of appetite exists - then you are looking at gastritishttp://www.peteducation.com/article.cfm?cls=2&cat=1571&articleid=438
Gastritis is basically inflammation of the stomach - and can be caused by consumption of bad food or indiscriminate things, bacteria, virus, IBD, or insufficient digestive process (lack of enzyme and maldigestion).
To treat, feed beef or chicken broth with 2 tablespoons organic honey melted and mixed in, with 5 capsules of slipper elm. In honey, further give probiotic, slippery elm, and marshmallow root - which is highly coating. Do not stop the probiotics ever for this boy - he will likely need them for life, as well as digestive enzymes. These are all cheaper than the best remedy I have found which is Digestinol with L-Glutamine. Many balk at the expense and large quantity size however but always an option.
Now the diarrhea is either originating in the small bowel or large bowel - it is important to distinguish where as they have different implications. Small bowel is urgent, watery......of
ten shooting water or pure liquid. There is weight loss with this due to lack of nutrient absorption.
Colitis on the other hand is the large bowel and this is usually "cow pie" like, rather than watery - usually mucous is present, and the dog may strain. There is rarely weight loss or change in activity level with this, since critical nutrient absorption occurs in the small bowel.
Colitis is often a symptom of allergies - environmental. It can also arise from IBS or IBD - common in this breed due to immune deficiency. A common symptom of these is that you will see an apparent recovery for weeks or months only to have it recur. Traditional vets believe this is a life long disease and about managing remission.
Given the stomach involvement that you have however there is likely something bigger going on than just colitis. If small bowel is involved with weight loss, you need to get vet attention as this can be life threatening long term.
I would not waste my money on fecal tests - they are far too often false negatives and do not rule out anything. Ultimately a waste of money except for the Clostridium test which is required to test for this toxin. X-rays don't show many things and also a waste...so if it comes to diagnostic testing - go straight for ultrasound and blood panel.
If Scout were mine I would:
-Go buy a digital thermometer and take his temperature via rectum - anything over 102 and I would head for the vet.
-I would begin the broth and supplements I suggest immediately - I would get the Digestinol which works wonders on gastritis and fast and allow 48 to 72 hours if the temperature was normal.
-If there is no appetite and further weight loss, head to an internal medicine specialist with ultrasound capability (regular vet not going to be much help and will just push fecals and Metronidazole which is not curative).