Gagging herself?!

My 3 month old started this new thing where she sticks her fists in her mouth and gags. Why is she doing this and how can I stop her? I thought maybe she was teething but I don't see any teeth popping threw and my older 2 didn't start getting teeth until much later. I have given her teething toys and pacifiers to try to replace her hands but she just yanks them out and sticks her fists back in and gags every time! This has been going on for 2 weeks now and it's an all day long problem!