What is the white bar above stamina for?
Solution 1:
Thus white bar is the charge left in your enchanted weapon (above stamina for right weapon, above magicka for the left) Each time you attack with your weapon, it use a charge, and the bar get more empty.
To add charges to your weapon, you first need a soul gem with a soul inside. Then, you must go in the inventory, select your weapon, then press the T key, select your soul gem, and your weapon should have more charges.