Pain

Hi again. Charley is now 7 months old. He was nuetered a month ago...all went well. A few days, or week, after his surgery he didn't want to jump up on the bed anymore...when he did he cried. Didn't think much of it because of his recent surgery. A couple of days ago, this started again. Crying for no reason that I can find. Just sitting and crying. He is obviously in pain. I took him to the vet today. Said he has a slight temp (1/2 degree) and thought it might be a bout of gastritis. Sent him home with antiboics. Also gave him a shot that said it would calm down his stomach. (he had thrown up the day before). I am worried because again, he doesn't want to jump up to the bed, or get in the car. Has anyone else experienced anything like this? Are there such things a growing pains in dogs?? I know there is a disease called pano, but, he is not exhibiting the signs (limping). If anyone can shed some light on this, please let me know. thanks