No energy to study

I have no Energy during the last period, no strenght and always feel asleep. I have reduced my workouts to 3 times a week (30-40 min a day) to have time and Energy to study for my exams but nothing has changed. I'm eating enough and often too much for not falling asleep on my books. I'm not sleeping well but I don't know the cause. I'm not stressed ... I was thinking about trying fb low impact to work out Everyday and boost my Energy and to not feel too sore for studying but I feel guilty about reducing my workout level. What do you think? What should I do with my sleeping problem and my weakness? Sorry for my long post. Thank you in Advance. I love the people of this community. You made me believe there is still love in the World for your support even not knowing each other