The problem you are describing can be because of something associated with the investigation done. The exact cause is difficult to pin point, but some time the colonoscopy
can cause some sort of complication which can present as the pain.
Another important thing is that IBS
is mainly diagnosed on the basis of clinical history and some investigation and rarely requires investigation of colonoscopy and there would also be no finding. So, if there is no other complication is there which you are facing with IBS, it is not required and as far as treatment of IBS is concern is mainly symptomatic in nature and depends upon the presentation. Also the best thing is to control by finding the food habit which is most appropriate.
Another thing which you ask about the steroid
is true that when something is not working and you are not sure for the condition, steroid is going to do the trick, at least for some days, but if the condition is not cured than it will reappear and long term steroid therapy can be harmful.
Thanks and hope you got your answer.