Under these circumstances, I would go to the GP, and explain lack of sleep, depression, anaemia, and how you're struggling.
I would also say to the school that you need your lunch break.
Making things easier, some ideas are buying more uniform to save on washing, don't have baths every night, if kids are 7, 9 and 11 they can definitely pitch in with tidying.
I would try every day to do something for you. Going for a walk at lunch break. Having some time in the evening for you, reading a book, having a bath, anything just so you feel you've got some head space.
Life is terrible without sleep though.
I can recommend Spatone for anaemia, it's much easier on the stomach and doesn't cause constipation.
Hang in there OP, you're doing an amazing job 