Hello and welcome to Health care magic
I am General Physician and additionally jr. to a Cardiologist. I read your problem in detail and wants to help you out. My first advise to you was to consult an orthopedician near you and get your X-ray Knee done.
If it shows normal study than you might be suffering from ACL (Anterior Cruciate Ligament
) tear of the Knee joint or other soft tissue injury
of the knee joint which might needs immobilization for several weeks. As you have explained you are in pain for several minutes while your Knee joint is involved in activity like walking, climbing stairs or even sitting on feets, rotatory movement while brushing etc., you have something wrong with your knee which needs to be investigated.
Consult your doctor and follow his advise.
Get well soon
Dr. Dinesh Kumar Bhatia
Health Care Magic