You already have good advice from other Elakiriyans, so I can only add a little bit about how memory works. Do you know that dreams are memory fragments that we were thinking about during the day and activities of the day? So when we are asleep, the brain will organize these memories in order of what their most used memories are.
So, if you are a student and are daily practicing something that will be prioritized and marked as the most important, hence easy to fetch, sleep is a must; revert your sleeping pattern to at least 6 hours of sleep. I usually go to sleep at 10 p.m. and wake up at 4 a.m. the next day, which serves me well.
For your exams, don't worry about exams; professors are lazy and usually give you old papers with a little bit of change, so practicing old papers gives you enough preparation for any exams.