12 month old baby cries a LOT, very fussy 98% of the time and only will stand on tip toes?

If i try to make him stand flat food he either screams or sits down, he is very fussy most of the time unless being held. I thought maybe he is just spoiled but he isnt held THAT much. His twin sister is a very happy baby loves to smile and is taking a few steps on her own now. He is just not a happy baby and if he does smile it lasts about 4 or 5 minuets then back to fussy again. She went right home after being born and he was in NICU for a short time (a few days). Oh, he also HATES groups of people, if there is more than a couple people around he screams and nothing makes him stop except leaving to a quiet room with him or going for a walk in the stroller. Anyone suggestions?