How much independent work are you doing?
The reason your teachers are going quickly, most likely, is because they expect you to do the majority of the work outside of lessons. So they go over a topic, you revise it in your own time, they go on to the next.
In further maths (Okay, you said "no further maths" but they're literally both maths) we've gone through 6 pure maths chapters, 3 mechanics chapters and 4 statistics chapters since the start of September. We have more lessons, but we're also just doing the actual work in our own time and that's what allows us to keep up.