How long?

NNEJ • 35 Yr old Mother of 2 girls and 2 boys 🥰💕💙

How long after bottom teeth are in do the top ones start? Since yesterday baby has been refusing to eat and is very fussy. Started a low grade temp last night. His older sisters both have colds so I’m not sure wether it’s teething or him getting sick. He won’t let me look at his gums.