You may get more helpful recommendations for resources if you specify which exam boards you are with.
Of those three subjects, I only did A level chemistry (Edexcel - I sat exams in 2022 and managed an A*). I also mentored A level chemistry (I have now mentored for most exam boards - OCR B and WJEC are the only two I haven’t taught yet) during my A level years and after, so I have some advice.
In chemistry, you will have a fair bit of maths. For example, you will need to be good with plotting graphs, reading relevant information off of them and calculating gradients. Furthermore, you will have to memorise a number of equations and know how to rearrange them. My experience is that students who did not pick A level maths alongside chemistry found these areas more tricky as they didn’t have regular practice with them outside of chemistry, but this was often remedied by giving them
this resource by OCR that works for all exam boards.
There is also a lot to memorise - colours of chemicals, chemicals and conditions needed for organic reactions, tests for ions and functional groups etc. As such, using active recall based revision methods are a must. These may include “blurting” onto a piece of paper, flashcards or regular practice with past exam questions.
I would also urge you to remember that you cannot possibly hope to study three A levels and come out with a strong set of grades if you do not have a healthy work-life balance. Have a routine that ensures you spend a
sensible amount of time studying per day
and some time to relax, eat and take care of yourself.
If you have further questions, feel free to ask away.