Source, Internet, disclaimer, not a medical or sleep professional. Use this only as hear-say.
Why do we need sleep - because we need to rest before our next conquest in life, which is tomorrow.
What our autonomous sympathetic nervous system does - it knows! It knows how nasty tomorrow is. We call this stress! Depending on the level of stress and ferocity or importance of the stressors, the nervous system decides that it is enough if you sleep for 3 hours in this time of personal emergency. So it wakes you up in 3 hours. But it is also kind! It produces cortisol, a pain reducing hormone so that, "hey my human, I woke you up in just 3 hours. So that you have 21 hours to solve our problems, so that we can have a happy future. Btw, it is painful, so I also spiked your blood with 500mg of cortisol so that you wont hurt". Sounds fair?
There you go. You are wide awake at 2.00 am, painless yet tired, nothing to do as the day hasn't started. Tossing in the bed.
Thus far we gave the definition of the problem.
What is the solution. We can go two ways.
We obey the brain. We get up, and do some meaningful work, and tell yourself, yeah, we did this so now my day is looking better. Then go to bed. The brain knows! So it lets you sleep another 3 hours. And you repeat. One day your problems will be really over. You sleep full night.
Second solution. Your problems may not be solved by you doing anything. Then, you do something to kill the cortisol. It is the baffle on which your brain is balancing your body. You knock it out. How? Vitamin C. It kills Cortisol. So take 5g of Vitamin C in drink form before bed. Take a drink of Vitamin C every time you wake. It should work. There are other Cortisol regulators, but none have the convenience, cost advantage and additional benefits of Vit C.