Knee Pain

[WD89]

I have sudden knee pain and it's freaking me out, because I haven't done anything (knowingly) to injure it. The pain is below my knee cap where it meets the shin bone. It only hurts when in motion...walking or using stairs, or anytime I have my weight on it. I have to limp because the pain hurts so much. Some days are worse than others; some times there is very little pain. When sitting down there is no pain, and I can move my leg around with no pain while sitting. My knee pops occasionally but nothing new. I'm in the military, and I don't want to go to the doctor unless I have to so I don't lose a deployment coming up. Any advice is appreciated.