Hi, there,

You have to move some of that milk, or you are at serious risk of mastitis. The quickest way to move some milk is to put your baby back to the breast. After you feed, put an icepack on your breasts - and take some pain relief - panadol or neurofen.
If you don't want to feed, you need to express some milk (breastfeeding will be more effective) At this point, anything will hurt. Feeding will hurt. But not feeding will hurt more. Your body was at the height of breastfeeding mode. Although you cut down feeds fairly gradually, it was a little too quick for your body.