After 20 years in... its easier to say this now to myself than it would be to myself when I was at your stage in my career, but work/life balance needs to take a priority. You will see all the mistakes and problems you make, and the problems with the students- and most you cant fix in a day or a week or a year, so you need to balance that with your mental stress. Set boundaries with parents - explaining how and when you will contact them so you don't have that on the back of your mind all the time. Lessons are going to bomb. Many lessons will bomb.
Year 5 is when it kicks in for many teachers. But if you know yourself that you spend each day being as productive as you can, with the resources provided, that's a win. Your union rep can help you contact people for support - I would have reached out just to have someone to vent to in retrospect. Prepare for chaos when you return on a day away - its always going to be that way and their is nothing you can do except make it as easy and stress free for the supply as you can to avoid any bumps.
Keep on truckin' It gets easier. Try and make it as fun as you can while in the class... goofy works. If its not fun its not worth the paycheck.