My dog keeps shaking and will not eat?

First of all yes he is going to the vet at 10:30am and if he gets worse they said to bring him in right away. I am just wondering if anyone had anything like this happen with their dog and if so what it was? I know it could be a bunch of different things I am just trying to get an idea to ease my nerves. This morning around 5am my husband got up and took the dogs out side then he feeds them and they come back to bed with me until I need to get up. So my husband came in the room and said Diesel would not eat (he ate fine the night before) so Diesel came back in bed with me and was shaking like he was cold so I put him under the cover and snuggled him next to me but he kept on shivering it took him a good 45mins to finally stop and fall asleep. Then i got up around 7 he was not shivering then I woke him up he jumped off the bed ran into the living room and laid down on his bed. Then after 30mins he started to shiver again. I pressed all over his stomach thinking there could be a blockage and I pressed on his spine lightly and so on with no response he just licked me. When the other dogs heard someone out side and were barking he jumped up stopped shivering ran to the door with his ears up and tail wagging. Now he is laying in his kennel and is not shaking any more but doesn't want to eat still (he did eat some treats though). I am guessing he just has an upset stomach or something but we are taking him to the vet to be sure. Does anyone else know what it could be? He is a Chihuahua mix and weighs 12lbs thanks!