I'd say that if you had a light workout and you didn't get the feeling that you've done enough, you can go back and workout again, but work a different muscle group. Try a circuit training or interval training set if you feel in the mood. I love those type of workouts. I feel great after a hard intense circuit training. If you workoutat a gym or someplace you can get on a bike, do a ten minute set on level 20 and super set that with walking lunges or etc.
You are going to see results in a little while, give yourself baby steps and attainable goals, don't quit, you will one day look in the mirror and see results. I have been on crossfit workouts for a couple of months and I have great results in my ams and shoulders and back with tone and muscle and definition, I too was a little discouraged at first, but it will come.
You will achieve more by baby steps and have fun while at it.