Hi, I'm also in year 12 doing my first year of A-levels. I'm not taking the same subjects you are; I'm doing Maths, Further Maths, Physics and Computing (so the exact opposite as you) and frankly I don't enjoy computing as much as I did in GCSE and I might even drop it. But I'm not going to come to that decision now and I think you should do the same. I think you should keep it until the end of the year. If you start liking English by then, you can keep doing it and you might enjoy it even more in year 13. What if you drop it now and then in the future, you realise that was a bad decision and you should have thought about it more? I don't know how much you hate the subject but see how it goes and if it is truly unbearable, drop it. And if you do drop it, don't be afraid of what your future unis might think. How about check what university you want to go to and check their A-level entry requirements for the course of your choice? Also, if you are thinking of doing a course in uni that heavily relies on English in A-level, are you sure you'll be enjoying those 3/4 years of uni?
About your mocks in December, there is nothing I can say other than revise. Try and make a timetable and do small 30 minute chunks of work (and have a 5 minute break abut every 1/2 hour) instead of sitting down for 3 or even 4 hours straight. The highest amount of time an average person can concentrate on one thing for is about an hour, so don't overwork yourself or you'll just waste your time and do less work than you would've.
Good luck and I hope for the best for your A-levels.
PS. Sorry if I made any grammatical mistakes, I'm not that good in English