I have literally just text my cdc about this (havent had a reply yet). I'm on day 7 of SS and yesterday evening I noticed that the inside of my knees felt very tender when I put them together, my thighs, bum(!) and tops of my arms/shoulders are all really tender too. It's fine when im walking around but its if i touch that part or sit down, it's very odd. I had it down to doing a 40 hour shift thurs/fri/sat when only a few days into ss, and without having anything but my 3 sachets x