As far as your GCSE grades go... focus on retaking those. I got one A one B and 8 c's. I know my grades are not the best and that is why i am retaking five of those GCSEs next year and try to achieve A*'s. As far as A levels i you will need to do smothing about that chemistry. Try and see if you can do that separate at another college. OR get your parents and sit face to face with your chem teacher, write a letter explaining how deeply foolish you have been and sell you self to get back into chemistry, if your that passionate about becoming a doctor then you should have no problem doing this.