Gets tired quickly

Hey,I'm in need of bit of a help here. I have to wake up at 6 and I usually get back home at 5 pm after my tuitions and school (6:45 am - 4:15 pm). And it's almost 6 pm when I start to study and within half an hour I feel really tired and I'll start to feel really sleepy after an hour or two and I can't finish studying. I haven't really studied in more than 5 years and somehow passed all of my exams but this is the most important grade so I really have to start studying. How do I feel less sleepy/tired and study for longer? Thank you in advance