As someone who has spent the last two months battling a foot issue myself, I will be the first to say that it is very difficult to say the cause. The reason, the foot is the nexus of all the connective tissue and muscles for the lower body, add in joints and bones (1/4th of all the bones in our body are in our two feet) and it is a crap shoot.
It could be plantar fasciitis but in my case it was tight gastroc and soleus (the two calf muscles) which led to inflammation of the fat pad in my heel. I had some Active Release (a special stretching technique) along with some acupuncture and taping and finally after 2 months I am on the road to recovery.
Any time we experience pain it is best to stop running--ice, elevate and compress and see how you feel after taking some time off. Running through pain without knowing the cause may cause you to unconsciously change your running form to compensate for the pain and you may create other issues up and down your kinetic chain.