You are not a failed teacher! You are a successful teacher with an illness and are not being supported properly by your employer.
Can you get an appointment with Occupational Health to get a programme of support/phased return?
My experience of crap support from school is thus:
I was off school with hyperemesis, for which I’d been hospitalised, and was referred after 6 weeks off. They were great. Suggested phased return to work when I was ready. School were useless and didn’t sort it out. The head was borderline aggressive in my back to work interview. I got as far as the staff room on my first day back and never even got up to the classroom before bursting into tears as I still felt so weak.
I went back off sick again, went back to OH and the nurse said she couldn’t believe I’d tried to return. She then signed me off for the rest of my pregnancy which was the right thing as I was still throwing up.
You’d think schools would be caring places but they’re just not. Not one person from school got in touch the whole time I was off sick (7 months) or when my baby was born or when I was on maternity leave; except from a card from my NQT mentor.
Don’t resign in haste - see the OH service first and see what they can offer.
If you are in school next week i hope it is better for you