Hi,
I think it is due to nerve compression at your lower back. You need evaluation of your hip joint by an orthopaedician and with help of imaging study.
Have you been to any doctor? If yes, which specialty?
Has any imaging study been done of your hip joint? If yes, then what is the report?
Where is your pain exactly if you have to point out with your index finger? As you have told there is radiation to knees and legs.
What is the quality of your pain (e.g., shooting, electric, dull, aching, etc.)?
Since how long back are you having this pain?
Do any positions aggravate or relieve your symptoms? Have you tried anything to help your pain?
Have you experienced any recent night sweats, weight loss, hematuria, urinary retention, frequency, hesitancy, or cough? Do you have a history of cancer, overseas travel, recent surgery, fever, or increased pain at rest?
Does your pain ever wake you up from sleep?
Have you had any recent change in bowel or bladder habits? Do you have any altered sensation in your groin, buttocks, or inner thighs?
Keep me posted with your answers.
Bye.
I have had similar problems---I suggest that you go for a nerve test to see the exact problems because you do not want to have nerve damage...also, an MRI of the back and the knee would help to focus the problems---these problems are more common for age over 60,sorry !!