I mean, define "hard". Like any subject, it depends what kind of brain you've got. Some people will find maths easy straight out of the gate, some find it really slow to understand. Same with history. It's intellectually demanding and has various technical concepts to get your head around. You will need to be good at constructing well-evidenced and logical arguments, and develop a clear and precise writing style. But the A-Level course is designed to teach you all of these things.
There's no point doing past papers until your teacher recommends it. You need to get to grips with both the content of the course and the exam technique before you start practicing.
But making notes as you go along is a good idea and will help with revision near exam time.