Does anyone else feel like theyre falling behind?

I started studying A levels in September. For the first few weeks I wasnt as productive as I didnt know how to study and most likely couldnt be bothered to figure out. But now I feel like im working longer than everyone else and still being so far behind. I'm studying more hours than the average work week (48h/week, including lessons tho) and it feels like I shouldnt have to study more hours than an adult works to still be getting Ds and Es. My parents dont see how much I study because im in my room and only seem to notice when im not studying (during breaks or if im being productive in other ways, like job searching) and say thats why im doing poorly. It's just really frustrating. It's also that the teachers set so much homework in such short periods of time, so I have to rush the homework rather than doing it thoroughly and understanding it, and then im almost going back after and actually doing it properly. It's really frustrating that theyre putting such high expectations on us and its actually making it harder. I'm doing poorly in exams as well but I feel as though exam techniques will probably be more focused on in year 13. I'm not sure, really stressed and dont know what to do.