Sharp pain in foot whenever iistep on heel. What could be wrong? Could it be a spur?

Heel pain. Most common cause is plantar fascitis which can be treated by ice, stretching , rest, injections, NSAID but i find orthotics help by taking the weight off the area.
Fracture or PF. Could be many things, but the two most likely are either a stress fracture or plantar fasciitis. The best way to know is to get an x-ray of your foot. Another clue is when it hurts: stress fractures are all the time, while pf hurts most with the first few steps in the morning, or after sitting for a long time. See a podiatrist to rule out nerve entrapment.
Heel pain. Plantar fasciitis (heel spur syndrome) usually goes away 90% by consistent stretching. Stretch or find a physical therapist that can help you with a stretching routine. The most common stretch is called the "runner's" stretch or "wall stretch". If pain is chronic, you may have other pathology rather than just tight/short ligaments and tendons. Hope this helps.