How do I know if my baby is teething?

my baby has had fever for 4 days now the highest 102.5F his got diarrhea and he won't quite eat as he used to he only takes my breast but wont drink juice, water or formula, also his naps or night sleep are awful been awake since 5am and its 8am now, his supper fussy and cries some times.

My boy just got a little restless in his sleep and his gum got a little harder a few days before it broke though.

lots of drewling,fussiness especially at night and you can feel a lump on their gums. oh a runny nose. some babies gums swell.