ETA: I was composing this before I saw your comment about the textbooks, RRiley99. It's rough when the prof doesn't follow a textbook closely, but even so, you may find that the stuff in the book can still provide a useful counterpart to the course material. It may have an alternate...
I'm currently in a mechanical engineering PhD program (sort of by accident), but my background is in physics. I like what I'm doing, but wearing dissertation-blinders all the time is kind of getting to me, so I'm looking for a place to get my fix of broader (but still technically-oriented)...
RRiley99, that sounds really frustrating. I'd like to ask a few questions to clarify the nature of your problem, so please bear with me.
1) What are the specific topics you're having trouble with, and what previous relevant background do you have?
2) What course materials are being provided...