In IBS gas puts pressure on the bowel and the bowel is pressure sensitive which is how it actually works. So the anitbiotic if you don't have sibo might help just by reliving gas pressure on the bowel, which in IBS is overly sensitive to all stimulis.
One thin about sibo and not ibs is absorbtion, in IBS absorbtion is normal.
You might ask for the test just to be sure that is what it really is and they use a hydrogen breath test. You don't want a lactulose breat test for it and they are not very accurate.
Even with sibo itself, without IBS the sibo can come back, because the sibo is not the actual probvlem but a consequence of another problem.
In IBS and sibo, they don't know yet how long to keep people on antibiotics and this is a real problem long term.
On the IBS research side they are still cautious of microscopic colitus a type of inflammatory bowel disease. But a good doctor can pretty much diagnose IBS with a 95 to 98% accuracy using the rome criteria for functional disorders, even though there is not a specific test for IBS yet.
There are some newer stool tests that might help and they use to seperate IBS from inflammatory bowel conditions.
Foods and stress don't cause IBS and the triggers can be different with foods.
On the stress side that is a different story, for one you might not feel under staress, but the symptoms themselves and the worry they can come on make a difference. There is an important aspect here called the fight or flight responce directly connected to gut function.
You should read these two excellent articles.
http://www.ahealthyme.com/article/primer/101186767
http://www.ibs.med.ucla.edu/Articles/PatientArticle003.htm
It doesn't have to be "stress' but just emotions themselves. Not to mention living with these conditions are stressfull and emotional.
But these have a direct and close impact on the gut, that a lot of people don't really know about or understand very well.
Sleep is very important to IBSers and they have found that quite a few IBSers have problems with rem sleep.
Do you have insomnia?