The thing about the scaphoid is that the blood supply runs past it then loops back. (poor design?) Anyhow, a fractured scaphoid is a nightmare injury given that its such a small bone. It heals quite quickly (leaving pain over the site (in line with your thumb at about wrist level) and weakness in the wrist in certain postitions. It can also cause thumb pain.
Problem is, if its healed slightly out of postiion (as fractures have a knack of doing) then it can put pressure on the blood vessels reducing peripheral circulation to the bone its self and areas distal to it. (this is a problem.)
Unfortunately, if it gets worse you can get all kinds of horrible symptoms (including pain, numbness, weakness and spasms), usually treated by corrective surgery.
In the past this fracture has been poorley treated and it is no coincidence that a high proportion of legal cases against A&E units relate to hand injuries which have been misdiagnosed.
Good news that its not arthritis, X-ray may well (hopefully) come back negative, but X-rays don't tend to show blood vesels too clearly. If the pain keeps on, keep on at your GP, if the pain is specifically over the scaphoid then thats quite indicative... Exercise shouldn't cause any new problems, but stop if it hurts, load up on Glucosamine and cod liver oil and try wiggling your fingers and keeping them warm (if it is blood flow)
Good luck and hopefully it'll just go away in a week or two!