Help - 6 month old baby won't drink milk

My baby is turning 6 month old, and he usually has a very good appetite. Yesterday and today his milk intake suddenly decreased. Of a 120ml bottle he will only drink 20ml. He doesn't seem uncomfortable, and just plays with the teat and smiles without sucking; or suck a little then tries to scramble away. We had tried varying the milk temperatures, changing location and dimness of the room. He doesn't have a temperature or bloatedness either. He just genuinely seem like he has no interest in eating. He hasn't started on solids yet. Does anyone know what may be the cause and if there's any cause for concern? #1stimemom #advicepls #pleasehelp