Suggest Treatment For Pain In The Back Of The Knee

I fell playing soccer 2 months ago. The back side of my knee where my calve reaches the knee has been sore ever since. I was boxing the other day and I agitated it and now its quite sore. It feels like I pulled a muscle but its on the back side of my knee, not the knee itself. Not shure what I should do. I am 23 years old, 6 feet tall and 160 pounds.