It's not chronic fatigue. It's just, when I'm sitting alone in a booth for 12 hours straight, I go insane. I'll get bored and tired. I lose my attention span entirely. I can force myself to study. But I'll put the books down a thousand times, and I'll usually forget what I studied. I need some external assistance.
I want to study 12 hours straight, focused, and alert, while retaining all of the info.
Step 1 is waking myself up and being focused and alert. Then I'll worry about the step 2 memory/comprehension part. Which I'm assuming modafinil could help.
12 hours of straight, focused studying may not be very realistic.
Break up your study time into manageable blocks of strong focus instead - find your sweet spot. The brain is not like the machines we humans construct, it needs some TLC and trickery.
My most focused and effective studying during university consisted of 40 minutes of playing a computer game, and 40 minutes of focused studying. 15 minutes break after each 80 minutes. This was a schedule a friend and I developed, and it worked really well. We would take turns at the computer and with the books.
We would also sit down to explain to each other what we had been studying. Discussing it forces you to organize the material effectively in the same way you would need it organized during a test.
Just by being in the same room with another person created positive pressure to study. During gaming, my conscious mind was taken completely off the study material, which I theorize helped the unconscious mind digest it.
Maybe a less sedentary activity than gaming would be even more useful, to avoid sitting for too long. But it would have to be something you really enjoy doing, and not too physically strenuous.
So the idea is less actual time put in with a higher degree of focus. Remember it is the end result that counts, not how many hours of study time you put in.
Also, instead of just passively reading the study literature, try to find ways of making the study session active. For example, rewrite summaries of what you read (by hand - typing does not engage the brain as effectively. If you also create shapes or doodle on the page, your brain will find the text more interesting and may actually remember facts based on their unusual presentation on the page or because of the funny face you drew next to it, or whatever other device you can come up with. Go crazy trying these things and see what works for you.) When rewriting, use your own words. This forces you to actually understand what you are reading, because you can not summarize something you do not comprehend. Read one page (or one section - find what works best), then summarize it.
Just taking nootropics is unlikely to help much if you do not use other little devices to tickle your brain's fancy.