What is this pain on outside back of knee with calf pain?

[KD520]

For a little over a month now I have been having this pain on the back side of my right knee towards the right outside.  Imagine wearing a pair of jeans and I am talking about the seam on the outside.  The pain gets bad and seems to radiate down to my calf.  When I wake up in the mornings sometimes it is so bad that I take nearly 20 minutes until I can stand and walk other days I am a little shaky but can go.  the pain gets almost unimaginable when I sit for say more than 30 minutes which I do alot since I am an ESL teacher and have to sit for sometimes 2 hours to teach a class.  The pain sometimes lessens after standing and walking for about 20 minutes and other times it takes hours for the pain to stop.  
A little more info to help anyone who might want to help me out.. I am 41, 5'4'' and overweight at 222lbs.  I smoke and my exercise is walking to the metro or bus and then walking about the distance of 1-2 miles a day at different intervals.  
I am wondering if anyone might have any clue as to what is happening here.  Its a bit hard to go to the doctor here in Turkey because they love to take foreigners money and really do nothing for you.  So to have a bit of an idea as to what maybe is the cause could save me time and precious money.  

Thanks in advance all and get well soon all♥