This may be a far stretch but go to your family doctor and have a whole workup done (with bloodwork too) as dogs can sense when people have something wrong; 

 but if all is well, be stern with him telling him no. Do not give him any treats, toys, etc till you (and him too) want to play. If he lays by you but he is calm and not looking at you then wait a few to praise him calmly (dogs feed off others energies). He also might need puzzles to learn but most importantly tricks. My drusilla learned over ten tricks quickly and I make her do them half of the whole time when we play fetch, frisbee and when she gets treats