I do have a very different opinion from previous people....
In fact self-study A.maths is not very difficult, but you must make sure that your understand the path that A.math do....
Self-study does requires patience, in other words, you must expect youeself to spend certain amount of time to study that subject. In addition, thinking is another important factor, so keep on thinking would help....
In fact self study has advantages, one of these is that you can adjust your study style according to your ability (of coz, do not spread it over long....long time, or its useless....), you can find a way that suitable your need, besides you may develop lots of your problem-solving techniques that your school teachers unable to teach (this is very important for you to study higher level maths in future). So you may consider self-study as a choice.....
One last thing, I believe that some math teacher in yr school must know sth about A maths, if my assumption is wrong, then its better for you to self study Maths too....
anyway, gd luck~