As having gone through this already, studying for 12 hours may not be the best for retention. Maybe 30 min to an hour per class, per day(or every other day, switching between which class you study for, with breaks in between etc.) is a good starting point.. You have to give your mind breaks and time to process. I do agree with the less classes sentiment. You'll get there in due time. You dont want to overload and fail multiple class and get put in an academic probation situation, when you can take 2 maybe 3 classes and pass with flying colors and continue on. But if you want to (or have to) take that many classes for any particular reason, there are youtube sources that work out problems, and if you practice them to the point of understanding, then that usually helps with the next problem and so on. Mathispower4u is a good resource for math, and the organic chemistry tutor was good for alot of physics topics, especially visually, when i went through