Hi, I am currently using Invisalign to straighten up my teeth, however, i haven't felt any pain or discomfort at all, the trays don't feel tight or anything and i am upto my 6th tray now, I would like to know if it is still working although i don't feel anything or notice any difference? Are they of low quality? I am paying over $7000 for them so i thought they will be the best quality but not sure anymore.