Aw! He's jealous of the new baby. He was the only child for so long and now I suppose he feels left out when you are giving the baby attention. The only thing I would know to do is to try different things, such as sitting on the floor with the new baby and include him in some play at the same time with the baby. You do have two hands!
Just try stuff like that. He's still a puppy and he feels left out and placed into the second spot now after being No. 1 around the house for two years. I would try my best to play with him and the baby at the same time (when you can) because I think he will learn to love the baby that way and not be so jealous.