Cant put weight on my wrist, why?

For the past year i have had recurring pain in my left wrist and cant bare to put any weight on it. This pain comes every month but last for a week or so. i can kind of move my wrist forward, backward, side to side, but when i try to bend it back or forward all the way it hurts. i can not put any weight on my wrist or lift anything up. i have ruled out tendonitis. my symptoms seem to match that of a ganglion cyst but when i bend my wrist to check for a bump, there is nothing there. i really want this pain to go away because i just recently joined the air force and dont want this pain to hold me back. if anyone has any idea what this can be, your opinion will be of great help. thank you