Can my sixth form force me to drop A level chemistry after year 12 mocks?

I sat my end of year 12 mocks in July of this year (2024) and didn't perform as well as i had hoped. I got a U in chemistry but I passed my other two a levels (biology and psychology). I also got a U in chemistry in my February mocks and in my resit exam following that. Due to getting a U grade 3 times, my school aren't allowing me to continue with A level chemistry now in year 13. Instead, they have placed me on a BTEC national extended certificate in business alongside a level biology and psychology, which has no correlation to what i want to do and was also the only option given to me. I have had aspirations to apply for pharmacy at university since very early on in year 12 and this is impossible without a level chemistry. Also, the BTEC in business is only equivalent to half an A level, which also makes applying to university harder as most unis require 3 A levels. My reasoning for continuously failing chemistry is due to several health problems that leave me in constant pain and fatigued and in turn making it difficult to attend a lot of the time. Due to this, i have also had huge problems concentrating. This has caused me to have problems with my mental health which i wasn't receiving help for throughout year 12 (due to waiting lists etc). All of my mental and physical health problems have been explained and proven to my sixth form but they will not budge on allowing me to resit. I have asked if i can enrol in BTEC business alongside resitting chemistry at the beginning of year 13 but they refuse. I also explained that if i were to fail the potential resit at the beginning of year 13 then I would happily drop chemistry and continue with BTEC business.
Now it is the beginning of year 13 and all of the support I need regarding my mental and physical health has been put in place by my GP. Again, all of this has been explained and proven with medical evidence to my sixth form by myself, my parents, my surgeon and my GP yet they're still not allowing me to try again. This is really disappointing as now I have to re-evaluate my options and give up on a career that I have been so passionate about for so long and have put in so much work doing summer schools for and online courses etc. Also, retaking the year is not an option for me as when i finished secondary school I couldn't start sixth form due to being in hospital which resulted in me taking a year out of education. Are my sixth form allowed to force my subject change?

I'm really sorry to hear about the challanges you've been facing, both academically and with your health. It sounds like you've been through a very tough time, and it's clear that you’ve made significant efforts to communicate your situation to your sixth form however while the decision to change your subject might seem unfair, especially given the medical evidence you've provided, your school generally has the right to make that decision based on your academic performance and the likelihood of success in future exams.
I’d reccomend that you either appeal the decision, have your parents call and email, consider a different course but it seems like you’re very set on pharmacy so maybe not that, or lastly resit year 12, it may feel daunting and you will probably feel behind but think of how great you will feel when you get the grades you need and since you’ve already gone through year 12 once, it will basically be a year of revision so you’ll have an advantage! Don’t give up on your dreams, you’ll just have to find another way to get there
Good luck and hope it all goes well ❤️