Hi there,
Warm welcome to the forum! Sorry to hear that you missed majority of your school days. It's must have been difficult when you had to drop out without school providing any other options.
Glad to ear that you are doing well in terms of health now. Do you know what's causing you to fall behind the studies now when you try to go back to it? Knowing exactly where you struggle will help break down any barriers you have.
Nowadays there's lot of online platforms catering various study methods making learning much more fun. They might help you fast forward yours studies and do them on your own pace while following recommended pathways. They require subscription but most of them has a free trial period to try out.
Few sites are as follows:
https://www.udemy.com
https://www.coursera.org
https://www.edx.org
https://www.khanacademy.org (this is one of my favourite, some courses providing helpful graphics)
Regarding exams, I've sat many exams myself but when studying a new subject or a hard subject it feels foreign every time. My best strategy is to practice answering exams in an exam set up at home. Meaning answering them within the exam time without looking up materials. If you can find past exam papers similar to the format you are getting that would be ideal.
Also I should mention that 2 of my friends' moms who were in their 50s went back to high school to complete their qualifications and successfully did so. Coming to the forum and asking advice shows how determined you are to complete your studies. That's a massive step in achieving studies.
Good luck and take care.
