Generally, your approach is okay, but you should be doing three quality workouts per week: Your long progressive run, your threshold run, and an interval workout.
To keep it simple, do the following interval workouts and just repeat them . 5x1000 on week 1, 6x800 on week 2, 10x400 on week 3, 5x1000 again on week 4, and so on. Recovery is 80% of run time on the 1000 and 800.... 100% on the 400. If you can't do all the reps at the pace you chose, your pace is too fast. Generally, the 1000 should start at slower than 5k pace and the last one should be faster than current 5k pace. The 800 should be 5k pace or faster. The 400s should be 4 seconds faster than the 800s, ie, if your 800 is 90 sec/lap, then the 400 should be 86 sec/lap.
For injuries, figure out the cause. Then, fix it. If you don't figure out the cause, you are doomed to repeat it. If you can't figure out the cause, post details here.