The first question is the big picture. What are your aerobic and anaerobic capacities?
What has changed from 6 weeks ago? Can I explain why I am running slow or not progressing?
What is my weak link? The purpose of this is to guide your training in the right direction.

The second question is how do you determine training intensity and volume for some training session?
You have some goal in mind for your daily training, and you know in theory what you should do,
but how do you execute it?

Say that you want to apply certain stimulus to your body. For example's sake, let's say that your
"threshold" is at 4.0 mmol/L or HR = 165. You want to run some intervals below your threshold.
If your lactate is 3.5, 3.6, 3.6, 3.8 for four reps, you used the right intensity.
If after your first interval you measure your lactate at 4.2, you know you are going way too fast
(but you may not know that when going by "feel", or if you go by HR).
If you are doing 6 reps and when you finished your 4th rep your lactate jumps to 4.2 (from 3.6 in your
3rd rep), you are probably done and you should not continue. If you did, you would be stimulating
something else, not the aerobic system as you planned initially.