Struggling at Dartmouth and no one talks about it

I am a sophomore and I have been struggling since the first term. I thought maybe its my major - which is partly true, i do better in some classes than others - but it isnt getting any better. I am always on or below the median and I work really hard for exams, they just never make sense. My understandings and their applications are plainly wrong no matter how much I try. I have gotten medians and below in all econ and govt classes. And it hurts. It genuinely hurts. Because I know that I am not stupid. I work hard and I was on top of my class. I never struggled this much with exams. I feel like I am doing something deeply wrong in approaching studying here. I talk to my professors at length but most econ professors don't have any advice for improving. What should I do? Can someone really tell me how they study? I ask my friends and do exactly what they do but it doesnt work out for me. I am always barely short of making the median. And the classes that I am good at, complit, geog, phil mostly, are A medians and i m never sure if i am good at them or if the professor was east. Help