Hi there, this is Dr. Elaine
This sounds like he is experiencing inflammation in his gut due to recent offerings.
Thankfully, he is young and resilient.
That said, the first thing to do is get the diarrhea under control. I am concerned he has had this for 72 hours--he may be becoming dehydrated.
Hopefully there is no vomiting. If there is or has been, with the diarrhea you describe, he needs to be seen immediately--he is too small to survive those kinds of fluid and electrolyte (potassium/sodium/chloride) losses without supportive fluids--usually given intravenously.
If there is no vomiting and he seems bright, alert, and his gums are moist (check this) then offer him water mixed with plain Pedialyte (half-half) until there has been no diarrhea for 8 hours.
The next thing to offer is bland food--at home this means cooked white rice mixed with either boiled chicken or lowfat cottage cheese -- mix them half-half, but offer only a teaspoon or so at a time--like every 1-2 hours and watch him to see he can tolerate it.
Over the next few days, as the diarrhea resolves you can start mixing-in his normal food--do it slowly.
I have attached a guideline for you:
Let me know if I may answer more questions.