Here's what my fibular stress fracture felt like...
I started having a little pain on the outside of my lower leg, a couple of inches below the fibular head. It would come and go, so I didn't worry about it. One day I was massaging my calf and discovered that I had a knot in the same area. It felt like scar tissue and when I pressed on the area it was sore. I told myself the pain was in the soft tissue, but now I know (having seen the MRI) it was really along the bone.
Meanwhile, I ran multiple races, set some PRs and was in the best shape of my life. It started to nag me more but was still coming and going at this point and was sometimes even hard to locate. Although I had had three stress fractures in other bones before this, I never even thought about it being one because of how fleeting it seemed and also because it was along the fibula, which isn't a bone that bears a lot of weight (it does serve at an attachment point for muscles, though, which causes a lot of mechanical stress). My other stress fractures had gotten progressively worse and, looking back at them now, I never really had any doubt that they were fractures. But this one was different. At times it felt like it was on the back of my leg while at other times I felt like more on the front, almost like anterior shin splints. It just didn't seem like a big deal.
Usually it would be a little sore before a run and then go away during, but I started to notice it more and more during the run. I started icing, foam rolling, getting massages - nothing seemed to work. Then I was running a marathon and just crushing it and started to feel a little pain in the area around mile 15. At 20 I felt kind of a popping sensation in my calf and had to stop running. I tried to stretch it and start running running again but could not stand on the leg. I literally went from running at faster than marathon pace to not being able to walk. I knew right away it was a stress fracture.
That night it hurt like a motherf$cker, so much worse than my other stress fractures. I got an MRI that week and it confirmed a stress fracture in the same area that started bothering me a couple months before, right where I found the knot. Rest it, man. Luckily, I was back in a little over a month!