I have bad heel pain, what is it?

Recently I have begun conditioning for the high school baseball season. This started in December and I have picked the amount of running I do by a lot. I mostly do sprints for about 10-15 minutes every other day. About 2 weeks into conditioning, I began to get really bad heel pain on me left foot. It is on the side of my heel in the outside. It usually always hurts at about a level 2 of 10. After walking long distances or sprints it gets to be about an 7.5 (10 being not being able to walk on it). I have worn get heel insoles in my right shoe to help with my Achilles tendon and just yesterday started wearing the insoles in my left shoe. I have not noticed any improvements in how my foot feels. What do you think it might be? If you have any questions that might help, feel free to ask me!