Still not sore?

Hi Fitness Blender Community!

I've been working out seriously with Fitness Blender for about 6 months now. Earlier when I had just started, I was sore almost every time I did a workout, and quickly gained muscle mass as well. Now, even though I'm lifting more and pushing myself (while keeping good form), I'm very rarely sore, and not gaining as much mass as I want to.

I've also noted that during my strength workouts, I have to take more breaks to catch my breath than to rest my muscles (it's more of a cardio challenge than a muscular challenge). Does anyone know what the issue might be? Thanks!