What is this pain in my legs?

Okay, im 19 years old & for the past few weeks I've noticed in my right leg that if I sit or stand for a long time that this weird pain would start. I can't pinpoint the exact areas on my leg, but it sorta feels like in the back of my leg towards my bottom, and around my knee somewhere and then maybe behind my ankle? It feels like maybe I strained it? But now my left leg is hurting the same way & the right one is not. And the pain is also in my left foot....I've read several things like, DVT or things like that, but surely not? I'm pretty healthy..could someone maybe help me out?