I did day 3 Level 3 today. I haven't been sore since the first half of Level 1, so you may not see the soreness come back, but if you're not feeling challenged it's definitely time to progress to the next level.
To track it search for "strength training" in the fitness tracker. There are moderate or intense to vigorous options. I used moderate for Level 1 and for Levels 2 and 3 I've used intense to vigorous. It might not be exact on the calories burned but it's at least tracking your minutes.