I'm guessing that you've now made a decision after 3 weeks of writing this post, but switching A Levels is really not a bad idea if you're not enjoying a subject, even if you've missed like 8 weeks or whatever. After all, you're spending so many hours a week on each of your subjects so you may as well enjoy them! I was in a similar position after ½ term as I decided to switch an A Level subject (to Psychology), there was lots to catch up on however I am now very much enjoying it and so all the catching up was worth it!