My breasts feel empty! Has my milk supply decreased?

Well, having soft breast doesn't mean that your milk supply has decreased. It would most likely means that you have fully expressed your milk and it's a good sign. On the other hand, if you do have engorgement, it might also be a good sign as it would means that they are adjusting to the demand of the supply. Usually, if you are direct latching, it is normal to feel this way cos baby is sucking well. Great job! Keep it up.