If you have the unaware incapabillity of sleeping, it is mostly considered as the main factor of "Insomnia", which is a common, temporary sleeping disorder, based off of general conclusions including stimulation, fear, other relating diseases/disorders triggering the incapabillity of sleeping, or simply not wanting to sleep.
Mostly, I'd consider improvising, and trying to go to sleep, or atleast rest yourself at short times. Essentially, 9:00 PM, or 7:00 PM. If you cannot fall asleep still, try sleep therapy, rather self-sufficient, or from a doctor.
Gravol; which is notorious for compromising stomach pains, or any abdominal distress, is also prone to cause major fatigue. So at a last desperation, I'd choose harmless medication such as Gravol, to try and influence fatigue in your body.