I've chronic sharp burning pain left lateral foot from base of 5th metatarsal knuckle up: it's not fractured. didn't know footwear faulty. what is it?

See podiatrist: One possibility might be Morton's metatarsalgia. A visit to a foot specialist would well be worth your time and effort.

Varies: There are a variety of potential causes including a neuroma or other pressure phenomena on the outside of the foot, a structural problem such as a "bunionette" of the fifth metatarsal, or even an irritation of a nerve in the back. Don't hesitate to be seen for an accurate diagnosis.

Of all the nerve..: I'm not quite sure what you mean when you say up.It could mean toward the little toe or toward the ankle. Either way, the nerves to consider are the sural, superficial peroneal or even one of the peroneii tendons. The irritation could be due subtle injury from shoes or lateral ankle sprain or kick. Have a specialist evaluate and offer treatment options.