My 3month old son has been spitting out his pacifier and trying bite everything else. teething?

Could be: Some babies start teething at 3 months . He may be fussier and want to bite things to relieve the pressure in his gums. Provide a safe clean teething ring for your son to chew on.

Who knows: A three month old usually doesn't have the physical ability to grab and hold a pacifier in their mouth or retrieve it if it pops out. They often manipulate it at random and it pops out, but they retain the need to mouth/bite objects as a self soothing ritual. It is probably just a random event.