yes you can exercise on ss and ss+. if you are new to exercise then the advice is to leave it for the first 2 weeks then do a small amount. i was used to exercise so just lowered it a little then got back to it.
that can happen. body can retain water. the weeks i've done nothing at the gym have been the best weight loss weeks. however you will be toning up when you do exercise and your sizes will change more dramatically.