I have started doing 4u papers.
I have done 2 so far and some questions are insane.
What can I do?
4u papers are known to be notorious but you should be able to get the feel of them after maybe three or four. If your still struggling, then it's a sign that you don't fully understand a concept or topic properly and thus you should go back and revise them, doing challenging exercise from cambridge, fitzpatrick etc.
If you look at the questions you struggle with in each paper, you will notice that each question is related to the same concept and topic, which links to my point above. I find that i struggle the most with mechanics and harder 3u type questions and so i have to continuously go back to the textbook and look over something.The key is to grasp the knowledge before doing practice.
Just do a lot more practice, under exam conditions, and mark your answers afterwards to learn from your mistakes. Worst case scenario, you can ask your teacher, tutor or even post the question on BOS.
Im sure some of the senior members can give you a better insight