So I am assuming year 12 is S5 in Scotland, well, you still have a year left. Try to stay for S6 or Year 13. 8 months in is too dangerous to switch subjects, you legit can't lose more than let's say 2 months of work. Take History at Higher, or Advanced Higher (AS or A levels) if you're able to "crash course" a subject. Depending on how confident you are of course. Trust your gut too, if you think History is your strength, and maybe you can get a career from it, then definitely do History next year. I am having a similar problem, but with Higher Engineering Science (or just engineering at AS level I think). I am one month away from my exams, I personally will not drop the subject, I will revise a little and hope for the best. If you think revising will take too much time from other subjects, drop the subject (Chemistry). Please speak with your guidance teacher or whatever you call them at your end. I wish you luck, comrade.