Great job on your composition! I am sorry to hear that your mind is so busy, but it seems that you have a good idea of what to do to fix it! I hope that you can get plenty of rest in the future. I have listed my corrections below in red! Keep up the wonderful work and I will see you tomorrow! 

Corrected paragraph:

One day, I noticed that I think too much about everything. From small to big, unhappy to happy, I spend too much time on meaningless thoughts. Sometimes, it is helpful to think long and hard before doing something important. However, I am sure I would think about things less than 5% of the time if I had to choose the important things. Especially because my memory contains sorrow, regret, and disappointment, which drives me crazy. Those memories always come to me when I go to bed and it disrupts my sleep. The worst case was that I couldn't fall asleep until 3:30AM. Yesterday was similar to the situation that I have mentioned above. I believe I have to move on. I need to evicerate all my bad memories from my life so that I can put my energy towards a better future. Time is so limited and I have a responsibility not to waste it. The past is the past and it will never ever come to me again. Therefore, I have to get rid of it. I believe that will also help me to sleep better in the future.