Heel Pain

Hi, I have fallen arches and whenever I walk a lot, especially in shoes with little support, I get these painful bumps in my heels. They get red and are painful for a few days/ a week. was looking at plantar fascitis but the bumps get red, a little bit swollen sometimes, and they are usually on the side of the heel, either inner or outer so I wasn't sure if that matches? What could it be? Any ideas would be appreciated! I cant take a good picture that would show the redness but I attach some