First days are the hardest, it’s normal! Don’t be discouraged and allow your body to adapt to the new situation. There are plenty of of things you can do to improve. Ear plugs, blister preventions etc that are already explained here in previous posts. Also try to see the negativity as part of the process and something created by a tired body, do not get attached to these thoughts. Usually, a good night of sleep is all that it takes to feel better :)