He is feeling jealous and left out, how about some one to one time without the baby so he feels special , let Dad take him out sports and outside activities, then you take him out shopping or something special just the two of you, also do things as a Family, get hin into physical activies, board games are great when Baby is asleep the 3 of you together again. Focus on his postive side and praise him when you see him doing something right..