The advice given by others (such as making sure you don't have an undiagnosed learning disorder) is useful. Here are some tricks I used in medical school:
Creating songs about a subject: "The radius is connected to the ulna. The ulna is connected to the humerus..."
Pretend to teach it to others.
Repetition, and repeat, again, and then once more. I usually need to read something 5-6 times to have everything fully committed to memory.
After class, immediately re-work the notes. Timeliness is key to clarifying information that you just learned.
Also, you mentioned taking multiple classes at once. Could you drop down to 1-2 this semester to see how it works with a reduced work load? Your post is well-written and clearly explained; so you clearly know more than you're letting on.