hip pain

im a 16year old girl and am very healthy and active. I dont smoke and i dont drink. I have been experiencing very sore pains in my right hip for the past 3years. I have had numerous hospital scans and nothing can be found except from a gap filled with fluid between the joint. The pain can be very intense but is usually like a pulsing pain coming from deep in my hip. I now also suffer pain in my lower back(on my right) and down my thigh, into my knee. When it is at its worst i cant walk but it isn't usually that bad. The pain comes and goes regularly and is not triggered by anything in particular except it seems to be worse in very cold weather. I have tried numerous painkillers from the hospital including diclofenac 50mg but these only help for the short term. do you have any suggestions about what the problem could be?