Week 10(5k) and 11(5k)

Week 10 and 11 were awful. Period and. First, during week 9 I had a really long run on Sunday, 20k, and felt good after, little pain in the feet but nothing I was too worked up about. Long runs leave you hurting a bit, I wasn't worried.
Come Monday I got right back on the horse and went to the gym to do a little lifting and a 5k warm up. As soon as I got my shoes on I noticed my foot was tender on the side, like... the outside of the foot opposite of the arch. Despite being tender I thought that I would give it a go anyways. I did the 5k and after spent the rest of my lifting hobbling around the gym on the ball of my foot because my foot was so tender. Obviously wasn't a good idea to run I guess. So I thought I would take a few days off, which I did, and tried to run again on Thursday. I got about 1/2k before I could tell my foot was sore and swelling again. Boy was I pissed. Week 10 and 11 fell during my winter vacation, which means I had tons of time to run, but was not able to. Despite wanting to pound my foot into oblivion just to teach it a lesson I sat it out for 10 days.
Today was the end of that ten days and the end of week 11. I went back to the gym and did 5k and lifted today. The foot didn't hurt or swell, but it did feel a bit funny. Now for the source of the pain. I don't know. It was not a gradual pain, it just appeared after the 20k, and then really throbbed when I ran on it the next day. I think it might be from the shoes I have been wearing, so I will try to get some different ones, trying to order some tonight, but otherwise I guess i will just stick to the shoes I think are good and ice my feet like crazy.