About the comprehension: could you try this - read the material 3 times - by the third time, you might comprehend it better/fully. I used to find that if I prepared questions about the material (as if I was writing the exam) - then this helped me focus on the important points in the material. Or try explaining some of what you've been studying to another person.
I used to prepare outlines for the various topics covered in my courses - making sure that I had included 10 main points (and then under each one - include 5 - 10 points) - to make sure that I had something to say about every topic.
To experience your interest and creativity again - maybe try a different medium, or look at some work of other artists and feel inspiration.

Or go to an art therapist? Sometimes they can help to unblock.