Hi there. This is pain due to nerve irritation and could be sciatica though this travels from thigh to knee, compressive neuropathy due to prolapsed intervertebral disc, nerve compression at the hip joint. It is advisable to undergo an MRI scan spine to check for any disc lesions, bony spurs, spondylolisthesis etc causing compressive radiculopathy. You might need an MRI knee or an arthroscopy of knee to look for any bony spurs etc irritating the nerves. Rule out b complex deficiency, hypothyroidism, diabetes. Multiple sclerosis, a chronic demyelinating disorder needs to be investigated. Hope this helps. Take care.
My guess is that you have an ordinary knee injury and fluid in the knee. The diagnosis isn't as sexy as spondylolisthesis, multiple schlerosis or sciatica, however it is one of the "rule outs". Sometimes this is due to a torn miniscus. You need an in-person evaluation. Often this problem can be solved by withdrawing fluid from the knee, which is examined for blood. This doesn't mean you don't have an exotic disease, but there is "ocam's razor". The simplist explanation is often the most likely.
I had a military injury with an identical presentation, and it was due to fluid in the knee.