i'm a novice runner so i'm not sure my input is the most accurate.
however, it seems to me like you're running without a plan in mind.
i remember reading somewhere about having your weekly mileage at the 80/20 ratio.
80% of your run should be in z2 (easy run, LSD) and the 20% should be at z4/z5 (threshold, interval, hill sprints) or something.
strength training at least 2 times per week as well to improve running efficiency.
i have only been doing z2 runs mostly and like 1-2 threshold run per month as i'm following the TAO training plan. i have seen massive gains in my speed and endurance. i think that is also because i am a beginner runner as compared to you. i think you need a more structured training plan to see improvements as a seasoned runner.
thoughts?
@Ender