Im a teenager who keeps waking up at night. it started suddenly and it has been three weeks. i was stressed but not anymore, what could be wrong?

Insomnia: I am so sorry to hear about your sleep problems, I know how frustrating that can be. Things to do to try and get back on a normal sleep pattern; No caffeine after 2 pm. Develop and maintain consistent patterns - go to bed at the same time each night. Don't do anything else in your bed besides sleep (no TV, Texting..etc). Try some relaxation techniques.If you continue to struggle, see a doctor.

Wake -sleep cycle: Often stress will lead to insomnia and other sleep disorders. Because of the length of sleep problems, you have altered your normal sleep cycle. Even when the stressful event is removed, the sleep disruption can remain. Try to get more exercise, avoid caffeine and energy drinks, and consider using some melatonin until your sleep returns to normal. If this isn't effective, then see your doctor