I was sure I'd fractured something in my foot last week, I could barely stand on it at all!... a day later it felt absolutely fine! (and then I buggered it up on a trampoline)... I always seem to assume the worst when pain's involved
My initial response to your post meehai was that surely if the x-ray shows nothing, then it's not a fracture, possibly bruising or straining of something... but then havign read the other posts, I'm genuinely shocked to find out that stress fractures can go un-noticed in x-rays!!! I thought that was the whole point of X-rays! lol.
Sounds as if you're pretty sure it is a stress fracture (and others seem to think so too), would probably be well worth getting yourself to a physio or going back to the docs and getting a second opinion?