My 3 month old baby seems to always be laughing. What is she laughing about? Does she already have a sense of humor?

Awww that's a good thing! Babies have two main ways of communicating with their surroundings -- crying or smiling/laughing. If crying is a response to things that make them uncomfortable and a need for change then laughing is the opposite. Your daughter is probably always pleased with whatever's around her and that's why she laughs alot. Nothing is more awesome than watching a baby laugh and smile :)