Little worried about my 3 month old

Hi, i know he three months old but im worried that he isnt smiling at all not even those ones that arent real smiles like when fall asleep or fart lol he smiled i swearctwice his whole life and that was week he was born. He also doesnt seem to have a personality. I try to play and interact with him but its like talking to a brick wall. His twin sister though is full of smiles gets excited when she sees us or we interact with her. He does have colic so idk if thats playing a role in this. I just would like one happy smile or even interaction something to know he is ok... or am i just over worrying ( yes doc knows he aint smiling)