I'm 16, and my right knee has had issues before. but now, only late at night between maybe 1-3a.m. my left knee starts to hurt, and it is excruciating?

Knee pain: Knee pain, that is excruciating needs to be examined and have some testes performed most likely, such as an x-ray to start. Chondromalacia, also known as patellofemoral syndrome, is a type of overuse syndrome common in young, active, often athletic individuals. See the dr. and get you excruciating knee pain evaluated. Best wishes.