Hi There,
How are your shoes? Are they old and worn out? If so, please replace them with good running/walking shoes, it is worth the money to take care of the feet. ANother thing is that you may have weak ankles. A way to strengthen them is to stand on one foot with the other foot held out in front of you. This is balancing act and if you need to hold onto something until you can do it go ahead. WHen you can do this on your own you will feel the lateral (side to side) muscles working. I run many miles (mostly on trails) and I perform this exercise to prevent ankle "roll out" on the trail. We are strong going in forward motion but the other muscles need to be strengthened too. I don't know what to tell you about potasium but I take 200-300mg per day. I hope this helps you and keep up the good work.
Maureen