Why don't I get sore the next day?!?

as you said, you are exercising for quite a long time now, the soreness and fatigue usually is experienced when you exercise for the first few days, (first time) or restart exercising after a long gap, but for you your muscles have tuned up to the exercises you been doing. hence worry not, as long as the effect is there, there should be no soreness and you are on the right track