Why can't I sleep at night?

Maybe because you aren't tired enough? You could try exercising more so that you get more tired at night. It could also be that you weren't able to do much during the day so you try to do things at night and that ends up shortening your sleep time. Personally, after I'm at school and practices during the day, I find that the only time I can pursue my hobbies or just do whatever I want to is at night. I'm trying to set my limits as to when I fall asleep because it's been hard to wake up early in the morning if I sleep at, like, 3AM. I don't know what it is you're having an issue with but, anyhow, hope it gets better for you. :)

Lots of people have trouble sleeping. Being under a huge amount of stress causes a hard time for people to be able to fall asleep at night. It is important to try to decrease the stress in your life as much as possible but if unable to it's best to add something in your life that will allow you some peace right before bed. Sometimes it may not even be real-life stress but more trauma-related stress. At that point, it is better that you see a professional preferably one that specializes in post-traumatic stress disorder. Sleeping allows the rest of the body and mind allowing an individual to feel better.