a level stress, sadness and hopelessness :(

honestly the way you’re feeling is totally normal! everyone is in the same boat and you have to remember that it’s only the start of year 12, and the grades you’ve achieved already are great for just starting out!

have you thought about an organisational process? writing down when tests are happening or when work is due, and making a timetable of when to revise etc? it sounds silly but being able to cross things off makes the weight lift off your shoulders?

im sure you’ll be fine

In year 12 I started off with DDB, then gradually made my way up to A*A*A* by the end of Y13. Everyone learns at a different pace, and quite often it's exam technique rather than differences in understanding on knowledge, which impact tests the most at the beginning of sixth form. But you do sound like you might be a bit burnt out, so I'd suggest making a plan of action for the next half term (such as organisational techniques, study techniques, when you're going to rest, etc), and then taking some time off just to recalibrate, regain perspective and start enjoying life again. Something that might help is if you try to read (maybe even make notes on if you have time, but it's likely that you won't!) the relevant textbook chapters for the week the weekend before you start a certain topic. It means that the lessons aren't introducing completely new stuff and that you can use them to really ask your teacher anything which still doesn't make sense, and to get to know the processes rather than just making loads of notes and getting used to the basic concepts.
It will be ok, and you need to look after yourself as well as worrying about work. Have some time away from your phone maybe, go out for a walk or just move away from the books for a bit, and hopefully, you'll start to feel a bit bitter. Things will improve, it's just a case of settling into the self-study aspect of sixth form and getting to know how your brain works and how you learn best.

My daughter did your subjects and I helped her to get started with organisation. For us, if we have everything organised and in its place then we feel more in control and less stressed generally - you might not be the same so this might not help you at all

We did a number of things right at the beginning of yr12
- printed out the exam spec for the sciences (I think the maths one wasn't as useful)
- bought the revision guides for the correct exam boards
- bought up to date text books for the correct exam boards so she always had them at home
- made folders for each subject with dividers for each topic in the spec - the revisions guides broke this down very clearly.
- got hold of every past paper we could lay our hands on
- once a topic was finished in class it got filed in the right place in the folder. School seemed to jump about a bit between topics and there was overlap so some notes got photocopied and filed in more than one place
- once a topic was finished she tried every related question she could find in the past papers or in the revision guide. Quite a lot of past papers come with marking schemes so you can see how many marks you would actually get given for an answer. If she couldn't answer a question fully then notes, text books and exam spec were referred to to see what she was missing. The questions/answers/revisions were filed at the end of the topic. Flashcards or mind maps were made at this point.
- once a topic was finished she highlighted the parts in the exam spec that she was now happy with - easier to spot gaps that haven't been covered at the middle of yr13 in case she needed to teach herself those bits.

All of this meant that going in to revision didn't mean starting to make flashcards and notes - that was already done along the way and they could just be revisited. You need to bear in mind that schools are often still teaching right up to the last couple of weeks before study leave - you will not be going back over all these topics again. Once you finish a topic you move on - if you can't answer the exam questions while it is fresh in your mind then that is the time to act, not a year later.
It took a lot of paper, a lot of printer ink and a few book purchases but it worked for her as that is how her mind works. Some people would run screaming in horror from this sort of control freakery!
Have a think about what might work for you - you need to learn your subjects but you do also need to learn how to get top marks in the exam and that is a seperate skill.
Good luck