are you stretching enough? limit any workout supplements. limit calories or at least anything that wont burn off quickly.
Dang, 5'8" at 157 and you're worried about gaining mass? I'd suggest just doing the things you enjoy doing and not worry about gaining mass.
THe probem I have with workout advice is that everybody, both expert and amateur, seems to have a contradictory opinion and the conventional wisdom always goes about 8 different ways. In that vein - here's some uneducated off the cuff advice, with no basis in anything other than guesswork: limit your routine to cardio, stretching & calisthenics (push ups (with your arms held in at your waist, not out as traitionally), sit-ups/crunches, and squats should do the trick). That's what m old thai boxing instructor always had us do , where staying around the same weight class, and hence not building too much muscle, was always a concern.
What works for some might not work exactly the same for others. I don't think ALL opinions are contradictory. There is quite a resemblance in most of of (ex: do cardio, high reps/low weights, eat lean spaced meals, etc...) I don't think it's rocket surgery.
