Clutch Problems

I just got a 2002 Cavalier 2.2 litre 5 speed the clutch is not working and it seems to be a different problem than everyone else is having. I have bled the clutch many times and it works for about 5 minutes and then it gets air in the system and the pedal sticks to the floor the thing that is confusing me is that it doesnt loose fluid the only time the fluid goes down is when i bleed the system so it is just sucking air and not leaking fluid i dont know what would cause this because i am not real familier with hydraulic clutch systems like these so any information would be appreciated thank you for your time