Noting that it is impossible to diagnose over the Internet, IMHO you have nothing to lose if you check your vitamin B12 level, as your knee condition seems to fit the list of neurological symptoms of the B12 deficiency.
There is a great book about the subject, "Could It Be B12?: An Epidemic of Misdiagnoses", so I won't try to explain the matter here using my own words.
Long story short: you should try to convince your doctor (or your parents should do it, as you are 16 only) to do the necessary tests (serum B12, Holo-TC, whatever else needed). Also, be advised that the currently accepted "normal" levels of B12 are way too low according to many experts, so you should rather try to educate yourself/your family about this topic before by e.g. reading the above-mentioned book. B12 deficiency, if you have it, is easy and cheap to control, but left alone it can easily wreck the havoc.