I Have Very Poor Reflex In My Right Knee And

I have very poor reflex in my right knee and I also have pain in this leg and have had 4 different diagnosis so far. One doctor said it was tendonitis another doctor said it was tendonitis and bursitis and a pinched nerve, another doctor said it is sciatica and a physiothereapist said its a pinched nerve in my back, he also said that this poor knee reflex means a dead or dying nerve, soooo how serious is this and is he right?