My Yellow Lab Is Experiencing Something But Not Sure What,

My yellow lab is experiencing something but not sure what, he just turned five...has no interest in playing, sleeping a lot. Sometimes when we give him a hug around his chest area he yelps then shakes. Acting afraid. I have not witness anything where he may have been injured. He is a very spoiled and loved boy and I am worried! Urinating and bowel movements are normal, still eating the same. Any thoughts?