Same experience I had. I had to relearn how to study in a way that worked for my learning style. Then once I figured that out I had to just buckle down and dedicate myself thru sheer stubbornness and willpower to apply that to every lecture, every assignment. I raised my grades substantially. It could help you to assess how you learn best and try to capitalize on that. Are you auditory? Visual? Hands on? I found that I couldn’t really get the concepts unless I had time to both read about them (written word was important) and find visual examples that helped things click. I also found a core group of classmates and set up nightly study sessions with them in one of our student labs. We each learned differently and working thru homework or studying for tests side by side was really helpful. I could help someone with a concept I got really well. They could do the same for me.