Harley has been acting like he has a stomache ache and I can't figure out why or what I should do. It doesn't seem to hurt him when I palpate his stomache but he keeps looking back at his belly and he is really lethargic tonite. He wouldn't even eat a treat!

There is no diarreha or vomiting at all and his temp is normal, gums are nice and pink and so are his eye lids. As far as I know, he hasn't had anything but his own food. Any ideas?
If he isn't better in the morning then I will be taking him to the vet but just want to see if there is anything I should do tonight.