It sounds like he's teething with a vengeance, poor baby. Mama's breasts are the ultimate source of comfort so it's no surprise that he is looking to you for relief of his pain. I wouldn't wean if you can help it because his teething won't last but the benefits of breastfeeding at least 2 years (minimum) will last him a lifetime.
Scolding him might just confuse him, though the natural reaction of yelping and a firm but loving reminder couldn't hurt. Making him wait 20 minutes is cruel and physically and emotionally harmful because babies have no concept of time and, if he's going through pain, you are his #1 source for the intense need for immediate comfort. Try keeping a teether nearby, or variety of teethers (including a wet knotted washcloth, or a wet soft cloth prefold, wooden teether, etc.) fresh out of the fridge so it has cooling relief. Maybe try letting him bite on it before and during nursing. If he starts to bite, naturally react then firmly remind him no biting, then immediately give him teething relief with a teether.
Hang in there. This too shall pass in the blink of an eye.
=)
M.