Suggest Treatment For Pain In The Knees While Standing Up From Sitting Position

     Hi, Doctor

From past 2 months, if I sit for 5 minutes I,ll have difficulty to get up and I fell pain at my kneecap and I lose control of my right leg for some second like 15-20 sec. I went to many orthopedic doctors but after the go through some physical tests they told every thing is normal and they gave me some painkillers and vitamin tablets. But nothing changed. Please suggest me what should I do.

Thanks.