Well, the pieces fit. I am pretty certain it is water on the knee, and that has several different causes, and the GERD thing and the gout are likely suspects. They fit well enough. Believe me, I won't tell the doctor what I think is going on. They probably hate that. I'll just tell him how I feel and the chain of events that lead up to this and then I will let him get stabby.
Also, if I were really paranoid, I would have worked in the causes that involve knee surgery.
I guess it could be flat out arthritis of some sort, but that isn't consistent with a few things.