I am in the exact same situation but in year 13 with the subject I hate because I wasn't allowed to drop it or change and as I had to re-sit my maths GCSE last year I didn't get to choose a 4th AS so it was a true nightmare. Anyway, change if you can because it hasn't gotten any better for me and its my worst subject too. Also, I do politics an its my favourite subject easily and its also my best. You really do better when you actually enjoy a subject.