Ask a Vet and Get Your Veterinary Questions Answered.
What you are describing is known as "acute abdomen". This is a result of visceral pain, which has a long list of possible causes. These include pancreatitis, dietary indiscretion or garbage gut, hemorrhagic gastroenteritis, foreign objects, obstruction, and torsions.
Since he is still showing signs of pain and lethargy, I would start by repeating the CPL snap. Being a Yorkie, I'm definitely suspicious of pancreatitis.
If this is still not positive, I recommend continuing diagnostics with an ultrasound of his abdomen. That can be very helpful in distinguishing causes of acute abdomen.
Even without a diagnosis, I recommend getting him into the hospital for supportive care. I would start IV fluid therapy, anti emetic injections (anti vomit drug called Cerenia), and eventually appetite stimulants and a bland diet.
I hope that helps.
Please let me know if you have any further questions. If you are satisfied with my answer, please click on the green Accept button. Positive feedback is always appreciated. Thanks.