Try to force yourself to think. I believe that you often can find yourself just spacing out and not actually progressing. You can try for example saying your thoughts out loud, or writing down all of you ideas, so you can keep track when you are actually thinking. Usually in A and B problems you have to understand 1 idea to solve a problem, but it becomes progressively harder to "one-shot" problems of higher difficulty. So try simplifying the problem at first. It also really helps me to constantly remind myself that the problem is solvable, because it is easy to lose all the motivation to solve a problem when it seems that it is impossible for you to solve it.

I started off in a similar place. One thing that helped for me to start getting problem Cs during contests was that I started writing down all my thoughts and observations while working on hard problems, no matter how trivial or unrelated to the problem it seemed. Eventually, I would have a list of observations and there would be a good chance some combination of those observations would lead to a solution, or at least the beginning of a solution. I think this helped because my thinking was unorganized before, and I would forget insights that I would have made earlier. Also, I started keeping a Google doc of difficult/interesting problems that I couldn't solve on my first try. I find that doing a short write-up of a difficult problem after you solve it really helps you to understand the ideas, which is important because that's what will help you when solving similar problems in the future.

Why this kind of blog again and again...
See my comment in this blog

Thinking is an acquired skill, and I have no idea why people tend to regard it as something that has a "shortcut." Do problems and you'll learn to think. the end.