Try and study hard for 30 minutes and then take a 10 - 15 minute break, to catch a breath of fresh air, and then hit it again. All extra credit should be automatically done. Those extra points may make all of the difference between letter grades. It also show effort and a willingness to learn which may sway the professors in determining your final grade. If your struggling seek out the extra help it won't come to you.
Tutors cost money but they are often more than worth the extra cost.
Some Universities offer tutorial services free or for a nominal fee. If you are interested in a tutor talk to me anytime during the semester. If you would like to be a tutor and have a 3.0 average or better come see me, you could earn some extra cash. Use your study time wisely. Do not pull an all-niter, it will not help your grade and it will make you sleepy and groggy during the test.