Been having sharp pain on the top of my foot, dont really know how it happened, it started yesterday and it hasn't gotten any better, i am always on my feet, stocking shelves from all heights. could it be extensor tendonitis? and what should i do?

Foot pain: It could be tendonitis. Other possibilities include a stress fracture or strained ligament. Treatment at this time would be rest, cold applications, elevation of foot while sitting, loose fitting shoes but ones that give ample support, and, if you can take them, anti-inflammatory medications like ibuprofen or naproxen. See a podiatrist for evaluation and treatment if no significant improvement.