Sometimes it'll show up on an x-ray, sometimes it won't. If it started recently, you should go back and follow up. Sometimes a crack or trauma to the tooth can result in it dying without any trace of a cavity. The infection can spread and cause the bump without it being apparent on the x-ray.
As always, the sooner the better because if there is an infection, it may spread. The sooner you treat it, the better the outcome.
Okay, thank you. How serious is this can it wait a few weeks or should i get it looked at right away. If I wait will there be any affects.