You're probably remembering more than you realize. More importantly, you have an understanding of the underlying mechanisms to intuit your way through many questions. We all forget things we don't use - I classically cite the quadratic equation as something we all knew once but probably couldn't recite from memory right now. Part of 3rd year is reminding you of things as you forget them, and 4th year and residency will continue to build on this so that eventually you retain the parts that are most relevant to your scope of practice. The rest you won't remember as well, but hopefully you'll know enough to know what you don't know and reach out for help as needed.
Many of the things you cite are not really step 1 material anyhow. The intricacies of pain management in the clinical setting goes beyond Step 1 which really just stops at the physiology of pain and how the mechanisms of action of the drugs involved impact it. You'll also find many varying views on the topic among the attendings you'll work with this year, often influenced by both their own training and the type of pain management they practice (ie. post-operative pain vs. palliative care). Pain mgmt is actually one of the things I personally feel very comfortable with and made a point to learn as much as I could when I was a student. Best thing I ever did: spend a few days with our pain consult team. Probably no time for that this year, but when you're a 4th year and you get to that point where nobody really cares if you even show up, spend some time with the pain team and you'll learn a ton.
Cancer staging is not really a heavy step 1 topic. I know they typically have 1-2 questions on it, but the intricacies of the TNM system are really beyond the scope of step 1 and ultimately the domain of specialists as the staging and requisite treatments continually evolve. One of the best things I ever learned about cancer staging came from one of my chief residents as a 3rd year student. He said that the key to understanding cancer staging and management was not to look at it as different stages of the same disease, but to look at stage 1 vs stage 2 vs stage 3 cancers as entirely separate diseases, as different as diabetes and sarcoidosis. Treating stage 3 cancer like a stage 2 makes as much sense as giving steroids for diabetes. I found that little switch made it easier to categorize things in my mind. Beyond that, best way to learn is to go to tumor boards and just practice staging the cases yourself as they're being discussed, and definitely try to stage your own patients and look up the current treatment recs on hte NCCN guidelines.
This is getting long but I think you get the point. You're doing fine. Focus on your patients and learning clinical medicine. Revisit some of the basic science as it pertains to your patients and it'll help it stick in your mind.
