My first metatarsal is hurting and won't heal?

About a month ago I was doing the 110 HH and after the fourth hurdle i landed and i hurt my left foot, which is my lead leg. My first metatarsal hurts whenever I put pressure on the ball of my foot. I researched online and it seemed to be pointing to a navicular stress fracture, but my doctor said nothing is wrong with my foot. I had an x-ray and an mri but nothing showed up. My foot hasn't gotten any better and i really want to get back to training. Anyone have any suggestions on what to do?