Sleep crying

My 1 year old has always been an easy baby. He can sleep by himself. When he wake up at night it is only for milk and will go back to sleep straight away. Only recently after his fever (mmr mmrv injection), he has been waking up in the middle of the night a few times. He will cry and cry as though he is in discomfort. Gave him milk and changed diapers and he will still cry so badly. We did notice a change in his appetite after his fever, he wont eat much nor finish his milk. I do see a tooth erupt but all these while his 6 teeth grew he has never been this way. He was all chill during his teething times. Only after this first high fever he didnt eat and sleep well. Anyone advice? tia #advicepls #pleasehelp