I have bad pain along the side of my left foot for few months when pressure is applied what could it be ?

Foot pain: Could be plantar fasciitis or inflammation of any of the tendons or ligaments in your foot. Have you been using any anti-inflammatory meds or been heating and elevating the foot on a regular basis?

Not sure?: Not enough information to answer your question, but any pain that last for more than 7-10 days that doesn't get better with rice: rest, ice, conpression, and elevation, should be looked at by a foot specialist.

Few possibilities: Including neuritis, tendonitis and stress fracture. Sine, your question is broad with "foot pain" , I am unable to narrow down the possibilities. My recommendation would be to visit a foot doc for further evaluation and treatment. Further walking may hinder healing and worsen your condition.