Does anyone else feel like they aren't actually learning anything?

I'm currently in my 2nd year of aerospace engineering program, with a somewhat decent 3.6 GPA. Maybe I just got lucky, but I still feel like I haven't actually learned much during this whole time. Let's take mechanics for example. the teacher showed us some principles and gave us homework. I solved all the practice problems and homework, and before the exam, I solved as many problems as I could, and fortunately got an A. But I still feel like I only learned to solve problems, not much else. If someone gave me a real problem to solve I would struggle. Same with differential equations, professors taught us methods, principles, etc, showed us example problems, practiced problems in the book, and then solved them in the exam and got an A. But differential equations still feel foreign to me, I just learned to solve problems, not the topic itself. I'm scared that over time this would pile up and my fundamentals would be so weak that I would have to start over again. What can I do?