Feeling worried

Hi mummies I’m feeling worried. My son 5 mnths just had his vaccination on both thighs yst.. after we came home his body was alil warm to touch and he rested about a good 2 1/2 hrs.. it was milk time when he woke up but he refused to drink.. usually his feeding is very 21/2 to 3 hrs apart.. but yst he the interval was 5-6 hrs.. he just refused to hv any milk n kept crying I believe in pain.. even when he drinks it was less than half of his feed.. Today morning he drank milk full at 7am.. next feeding supposed to be at 10. But he refused again.. I let him play awhile n tried to feed again but he refuse.. tome drag to 1130.. I gave half a grape smashed he eats it.. I tried giving milk again after it he refused n pushes the bottle away.. I changed the teat but refused too.. At 1200 No choice I decided to give alil cerealac mix with milk.. he refused it when I gave in bottle.. so I put it in his baby bowl n fed him.. he took about 10 spoonful and slept.. I’m feeling worried that he is not consuming enough.. it’s 5 hrs and he only had spoonful of cerealac with milk and half a grape.. what am I suppose to do? It is bcos of the vaccine his appetite is Low..