Did I sprain my leg??? Need to know?

Today in softball I hurt my leg while playing in the outfield. I was standing around and all of the sudden my knee hurt really bad. And it's been hurting all night. It's on my left kneecap, right on the side. It's a tight, ache kind of pain, but it hurts really bad. But I'm a teenager so it's not like I'm old and getting hurt all the time. Should I go see a doctor? Did i sprain something. And btw don't give ice as a way to help, cuz I tried it, and the pain is on the inside. Thanks for your answers.