chronic knee pain
gradually increasing over the period is most likely due to osteo arthritis it is nothing but age related degenerative changes which usually starts after 40's .
all uneed to do is consult a orthopedic surgeon ,get x ray to know the severity of the disease and blood test
to rule out other kind of arthritis.
If it is osteoarthritis
the main stay would be physiotherapy
and some anti inflamatory medications