Hello comrades and welcome to the third improvement megathread of June! 
As usual, some discussion ideas:
- Do you want to share something you've done in the previous week? Everything counts, nothing is too small.
- Do you have any plans or goals for next week?
- Do you have any streaks? For example, "sober for one day." Feel free to post your streak every day in this thread.
- If you don't have a continuous streak, did you manage to abstain from something for a day or more?
- Did you come across some useful information or resource that might help others?
Poster caption: Let the Chinese-Soviet friendship live eternally!
Good luck with your goals! 
This can be caused by a lot of things, no? Are you sure your running form is good? Small bad habits like over-striding can add up with heavy mileage.
I used to almost exclusively run for my cardio, but I reduced stress injuries when I mixed up my workouts. Run one day, swim the next, bike after that (where I learned that I really enjoy biking for exercise). Maybe some high intensity ab workouts too.
I usually do short runs (3-6km). I also don't do long strides just because I feel I can pace myself a bit better either short strides. I'll probably look into mixing up my workouts though.