Sometimes to break through a plateau I have to shock my body. This sometimes includes adding in a different type of workout...instead of running, I swim. Or workout 2x a day.
Changing up my eating routine helps too. Eat at the low end of calories one day and near the hi end the next.
2 a day workouts may include breaking up a 10 mile run into 5 in the morning and 5 at night.
Or, swimming in the morning and biking at lunch.
I always pack extra workout clothes JIC I can squeeze in another workout during my workday.