What Causes Constant Pain And Discomfort In Foot?

I get plantar fasciitis type pain frequently but the discomfort is not constant.Sometimes I forget about it and other times it wakes me up. I have had Sacro-iliac pain for several years and I feel like that is the reason for my discomfort in my foot. It is exacerbated especially when sitting for such a long time such as when driving for more than an hour. My doctor didn t respond to my concern at all. Thanks for your help