Sticking to it is the hard part, and I think it would take more than an app to make me follow a regimen. For me, my future profession requires being physically fit, so that helps with motivation.
I usually recover an hour after a workout before I feel like I didn't go at all, but I feel it the next day (sometimes another day after that). Or like Buff said, you could be taking it too easy at the gym. Soreness comes from tearing tissue.