How do i know if my baby is teething?

my baby is about to be 3 months old and i think she is teething cause she puts her hand in her mouth, i read that babies do that to give them comfort , she slobbers a lot .but im not sure if she is teething she doesnt have any fever or anything but from time to time shell wine like something hurts then shell put her hand in her mouth an start gumming on it how can i tell if she really is teething?