Pain in the beginning

I am on my second set of Invisalign alligners after using the first set for 3 weeks. As is always the case for any type of braces, my teeth were a little sore the first few days when I started with the first set of alligners. That's fine with me because I feel that means it is working. However, now into my second week on the SECOND set of alligners - there has been no pain/soreness at all. Does this mean the second set is not accomplishing anything, and may not be exactly the right fit it needs to be? Or is this normal to not always have pain when switching alligners? Thanks.