This is a tricky one, but I would say it's totally normal, I can assume you are only a few weeks maybe into your studies. I imagine all these subjects are new, daunting and seem impossible. I have felt exactly the same. I started with pof and GNav, they are two of the heaviest subjects in material, volume and understanding. I spent 6 weeks in each doing about 9 hours a week to get 50%, and I went to a selective grammar school, so don't worry, it's not lack of intelligence. The volume is simply too huge to fully understand in such short periods, to even try is foolish. And some of the questions are written simply to catch you out, not to test your knowledge. In short, they are a frustrating mess of poorly worded questions that make assumptions and use tiny wording differences to catch you out, hence your scores.
Recently a tactic I have found to be generating much better scores much faster is to read the topics thoroughly, and research anything that isn't clear, as stated via YouTube or the web, do the progress tests as desired, make no notes.
Use the BGS or other bank and use the sub topics inside the topic to focus on each section. I've been doing 40 questions or so across three hours and then making the notes as required, especially formulae and definitions etc. That way your learning is far more focused and ordered, in the material it is simply impossible to know what is essential and what isnt, after all there's only so many ways they can ask you how far away one latitude is to another or what track the aircraft is using.
For reference I'm now doing 12 hours in 4 days, 4 days at work where I may do another three hours if I can, and then 12 hours in 4 days. I've scheduled 18 months from start of revision to end of last exam. Until the brush up week at the beginning of June where I will possibly step up the revision if I can see what I don't understand until the exams in August.
After that it's simply a matter of playing their game and learning what the question is asking.
Keep at it, they are a rollercoaster of emotions and often feel like being kicked when you are down. It simply appears a matter of putting the hours in rather than any significantly difficult principles. Practice practice practice, but focus that practice.