hi
while i would advise to go and see your doc i would'nt go thinking the worst case diagnosis until u get one---people with ibs suffer from this all the time and it can be just related to spasms in the gut -or a knot in the belly as some say.
if u have ibs and have been screened probably by a gastro doc i;m sure it is just a flare up --if not go to your doc it is the best place to start and explain every detail to them
let us know what happens
you need to see a dr right away that happened to me three years ago and now i dont have a stomach it was cancer good by my friend