What you need to do when you return to activity is do it gradually. I would go to the gym now but do non-impact work e.g. bike, cross-trainer. Then as the pain subsides do a little bit of running, just until you feel some discomfort. Then gradually increase your running time as pain allows and you will eventually get back to what you were doing.

With the aerobics, is there a lower impact one you can attend. If not speak to the instuctor as you will need to sit out part of the class if the pain comes on.