you don't need to feel sore. if you feel and look stronger, you probably are. putting stress on your muscles will make them stronger as they recover, but that doesn't mean they are going to hurt.
but, adding a little variety to your workouts might cause some soreness, and can definitely make the workouts more effective. that might be something to try.
and, if you want to be sore, for some reason, go plyometric or slow cadence for a day...you'll feel that for a couple of days for sure.