Thanks for the query to H.C.M. Forum.
Only one thing is there that painful swelling around knee anterior & posterior side and weight increased.
One thing I don't know ,why your cardiologist advised more salt as salt present in all foods .
So your history is very ambiguous.
So get in blood for C B C , serum creatinine
, R A FACTOR ( for rheumatoid arthritis
) , osteoarthritis
Consult an Orthopedic surgeon and get his opinion for knee swelling and physician will find out the cause of kidney
Good luck. Dr. HET