Need tips from the readers

i have this major exam in may that'll decide my future and although I'm very serious about it i just cant concentrate on reading for example i keep yawning even tough I'm not tired, i watch a lecture for 10 min and get distracted and the major problem is i feel so sleepy all the time even tough I'm getting a good sleep actually more than 7hr and i still feel sleepy. In past i used to stay up all night to study or even read manga but now i cant even do that and whenever i go to sleep i feel so guilty thinking i didn't get much done for today. So I need your help guys please tell me how do you guys stay up late or how do you guys study for exam anything that'll help me please.