Depending on how you're lifting, what kind of method you use to lift (slow versus fast, for instance) soreness in and of itself is not an indicator of whether you're lifting enough. At the very least, REPS is a better indicator - if you're able to do, for instance, 20 reps at a given weight, that weight is too light for you for that particular exercise. Aim for a weight that you can do no more than 6-8 reps. When 8 reps at the weight you're using is or becomes too easy, increase the weight. At the last couple of reps you should be straining to complete them using proper form. If you're not, you're lifting too light.