Hopefully I will be slightly more reassuring but I do completely understand the first 2 responses ( and at times, would post similar).
Expectations are unbelievable, unrealistic and all consuming. You can never do enough and the 'tasks to be completed' list only ever gets longer. Criticism is much more prevalent than praise and comments about the hours worked/holidays etc will wear you down.
BUT
I LOVE MY JOB! It is hard, heartbreaking and demoralising at times but, ultimately (for me) it is the most exciting, fulfilling and rewarding job I can imagine.
The school, the head and your colleagues are crucial to whether the good days outnumber the bad. Choose your school as wisely as you can - it can make the difference between surviving or not.
How I think/ work - this works for me so may help.
Remember, ultimately, it is just a job. It is not you or your life; just a part of it.
Recognise you will work ridiculous hours during termtime and a chunk of time at w/e and in holidays, esp in your first couple of years. I work 7:30 to 6 Mon to Fri at school with a brief break for lunch and occasionally at w/e even now. During most week-long holidays, I do a full day in school and between 2 and 5 days in other holidays.
Be ruthless. Prioritise what needs doing - balance out the scariest demands with the tasks that will make you most effective with your classes - sadly these are not always the same.
Organise the time you have to complete these tasks and stick to it. This is hard but the bit that helps me the most. When I've used up all my allocated work time, I stop. What isn't done then, doesn't get done then.
Let colleagues support you with kind words, ideas, resources Tec. Be quick to support them back.
Be organised - files, folders, memory pen etc. Devise a naming/filing system than works for you and use it rigorously. Back up regularly. Try to deal with requests/demands as soon as you read/receive them. You look in control and you don't have to remember it later. Have a box (mine is large!) that you can put (hide) paperwork in when you start to drown under paper. Sort it at least once a month. Most important stuff will have been chased up or re-sent but I find it satisfying to action/ file/shred en masse every so often. Don't be a slave to your email. Check it daily and deal with it then. Check once at the w/e and once a week in holidays.
Develop some stock phrases you can say when asked to do something else that you just don't have time to do or ways to ask for help. These will depend on your personality and the school but I use " I can if someone else takes on X" and "No, that isn't possible" a lot!
Maintain your relationships, your health, your outside of school life by being ruthless (as above), organised and 'selfish' - you are a better teacher if you are sane, healthy and happy!
That's very long and does read more negatively than I intended but I mean it to reassure. As I say, I love my job. Like every teacher I know, I work bloody hard and stupidly long hours at times but I trade it off in my head because I earn significantly more than the majority of my working-class family could have envisaged; I do have more holiday days than the majority of my non-teaching uni friends and my day to day time with my class brings me an amazing sense of personal satisfaction.
Hope that helps, avocado