Something popped in the side of my knee when i crossed my legs to sit down. Now when i try to stretch it, it hurts. I did not pull a muscle because it would've stopped hurting by now. Feels like something's going to pop when I try to straighten my leg. Now I can't stand up. Hurts when I try.

I'm 16. This is the first time it happened to me and mom and I are not sure what it is. Anyone know what is going on? Cause I don't know what it is. It's not my knee, it's kinda at the side of the knee joint. Mom thinks I should try to straighten it but whenever I even try to sit up, a sharp pain develops there.