my yorkie is 17 months old. The past couple of days he is all happy and chippy in the morning and eats his food but at night he picks at his food and just lays around. just not himself. I gave him a small piece of pupperoni stick on sunday. Other than that he hasnt ate anything different. He is a month over due for his shots and hasnt had heartworm medicine in this time. Could he have stomach worms? Just getting concerned.