I had a similar experience with photography. I did alright at GCSE-level photography, but slowly got worse when I did A-level photography. That was because of multiple factors, including hating the other four people on the course, having utterly stupid tasks to do and wishing I was doing something else with my life entirely. When it comes to geography, why did you enjoy it when you were doing your GCSEs, and why aren't you now? Is it just because of the increased difficulty?