Welcome at HCM.
I have read complete details of your question.
It looks from your details that most probably you may be having arthritis
of your knee.
It is degenerative disorder of knee.There is excessive wear & tear of the cushion of knee ,because of this there ia pain on movement of knee.
You should not worry ,with advancement of medical science there are some remedies which can be helpful for you-
-You should start doing quadriceps exercises of your knee.See complete details in this regard at following web link-
-Avoid palthy or cross leg posture.
-Do warm water fomentation at your knee.
-Take a good analgesic
on your doctor prescription.Please do not self medicate .
-Take joint supplements like glucosamine
with chondroitin sulfate.
Hope this all will help you.
With best wishes.