What other subjects are you doing? It's not too late to change, my mate changed everything but geography in February of Yr 12, it took her a while to catch up and her AS results were less than she was capable of but that was only because she missed the Jan modules for her new subjects. She has now been accepted by everywhere she applied for uni & is on track to get great grades. Try speaking to your head of year, they will try & put you off changing course but explain that its better than dropping out altogether. I enjoy my subjects but there is no hiding the fact I cannot wait until uni, I think most people find through out the sixth form that the only reason they are still there is because they want to go to uni, you reach a point where you just out grow school! It happened to me just before my GCSEs, I know how hard it can be but keep your head down & work hard & you'll be finishing before you know it, it scares me how fast the past 2 years have gone! If you focus on your goals, uni, it helps keep it together!
Having a lack of things to do is never good! Again, speak to a teacher giving suggestions, I'm sure they'd be happy to help you get things going! As for unethusiastic teachers, ignore them! I'm always getting told off for poor attendance but consistently get better grades than those that attend more than me, I work hard on my own, its great preparation for uni and you can focus on what you enjoy, not what the teacher thinks you should enjoy!