I was in the same situation as you a few years ago op, and also was an experienced Teacher who had taught in a variety of different Secondary schools.
I knew from day one that I hated this particular hell hole of a school. The students weren't great by any stretch, and some were vile, but it was the attitude of many of the staff, and bullying tendencies of some that I couldn't stomach. There was a massive air of arrogance and bullshit about the place that we were all supposed to buy into too.
I cried on the premises, on the journey home, and at home on my first day, and every single day thereafter, I would cry at least once - usually in the school toilets. I started to take off a lot of time, as the environment, bullying and harassment I was subjected to was really taking its toll and making me physically and mentally ill.
I ended up suffering from stress, tachycardia and palpitations. My GP was amazing when I reluctantly told him what had been happening to me, and I burst out crying hysterically. He handed me tissues and a glass of water, and told me to try not to worry, as he was typing out my form to write me off on sick leave. I felt suicidal on some days, and if it hadn't have been for my GP, I dread to think what may have happened.
I was on one of those probation contracts too. Whilst on sick leave, I contacted and registered with several supply agencies, and told them I had a preference for long term work. I gave them the referees from my last place of employment (just asked their permission first and told them things weren't working out for me and that they didn't know me well enough to be referees in the new place). I was offered lots of work, long term and day to day. I took on one role for 5 months in a fabulous school, and whilst there I gained a promotion at another excellent school and started there after my supply contract ended.
Upon signing up for the role, I wrote a letter of resignation to the Head of the hell hole, and just told him my health was suffering there and it wasn't working out for me, and that I hadn't received support from line managers. I received a letter back within 2 days, accepting my resignation. I broke my contract, but they didn't do anything about it.
Sign up with some agencies (Hourglass Education were fabulous for me), and get the hell out of your school - do not get ill, and screw the contract - you are worth so much more!