Hey Sunnydays
Today is my 3rd day on SS too
Like you I've been going to the gym regularly for about a month before I started this diet. I was worried about exercising on such low calories as if I've gone to the gym in the past with not eating much that day (say I didn't have lunch or something) I'd find I didn't have the energy to push myself on the equipment, it felt like it was just too much to do.
So naturally I was worried about doing CD because like you I wanted to exercise and prevent loose skin. Anyway I spoke to my CDC and she advised me to steer clear of exercise for the first week or so to let my body adjust to what I'm feeding it (or not feeding might be a better term). After two weeks I'm going to start doing yoga & pilates classes at the gym, weights and also moderate swimming. Nothing strenuous.
I'm no doctor (I do study biology though
) and the best person to ask is yoour CDC but personally I'd say you are doing a bit too much. Our bodies generally (varies from person to person) need 2000ish calories a day when we are stationary and aren't doing anything, so to reduce calorie intake on CD to under 500 a day is pretty drastic. If you are burning say 500 cals walking and at the gym (I'd say you were burning a heck of a lot more though doing 7k of walking) that means your body is literally running on empty.
Toning anaerobic exercises, body brushing and moisturising should help against sagging skin, but the only way to completely avoid this is to lose weight at a slower rate of 1-2lbs a week so your skin has time to adjust. If you want to keep up doing so much aerobic cardiovascular exercise though I really don't think it goes hand in hand with CD as feeling dizzy, lightheaded or faint is never a good thing at the gym.