Taekwondo: I can't spar will because my instep aches from the kicks?

stop kicking with the blade of your foot then. its really simple because if you have been constantly doing sidekicks on the bag with the blade of the foot then its going to get sore. the only time you should use the blade(instep) is in a pattern not a real kick or dummie bag. in real case you use the heel of the foot,pack a lot more power then the blade(instep) anyways. i had the problem when i was a blue belt :P