I have a expander for 3 months. my 1st molar hurts a lot. i pushed down a little and i felt it move. i don't know if its the expander or the tooth. ?

Either: It could be either. You should probably have your dentist take a look. It could just be the pressure from the expander, a tooth that is going bad, or the expander pushing into the gum.

See Orthodontist: Please see the dentist, pediatric dentist, or orthodontist who placed the appliance. It's probably a loose appliance (from hard/sticky/chewy foods). Could also be from tooth displacement, traumatic occlusion, or cavity. Don't wait, call now.