FWIW, my father was born with one kidney and he lived to a ripe old age. People donate a kidney all the time and live a normal life.
Anything containing sodium can cause fluid retention, which can cause the ankles to swell.
The traveling joint pain and rash, though, are a couple of flags for RA, and it is not at all unusual to test negative in blood work yet still have symptoms. Ask for a referral to a rheumatologist, who specializes in all manner of autoimmune disorders such as RA. A good one will look at ALL the evidence, not just blood work.