3rd semester of physics so you're taking Modern Physics?
In any case, understanding physics and grasping the material means you need to have a well enough grasp on the mathematical concepts (calculus 1 +) that are incorporated into the course. Calculus doesn't necessarily have to be a second language like someone suggested, but you should be a good (B or above) student, and know the main points well enough to help you.
From what you posted, you haven't really studied, "...when I do, I do about the same", from what I gathered. Not only that, your method isn't the right method to help you understand the material. Studying isn't just about doing it on your own either, you can see a tutor as well to help you with the things you don't understand.
Also, if you are using one book, try and get a supplement to the course you're taking. We used University Physics with Modern Physics and that book was the only one I needed really, although I also have Physics for Engineers and Scientists by Giancolli, which is pretty easier to read from. But other than that, I also bought physics demystified for a rather brief introduction to all the major concepts I needed to know.
Finally, doing practice problems is a good way to help you understand the material. Write out several steps in solving a problem, then try a practice problem following the exact same steps, then a few more, and finally try doing more practice problems without the steps aiding you.
P.S. If you search the net, you can usually find some preview tests of the same course instead of being blown out of your socks once the paper is passed to you.
What is it that you don't understand by the way?