Cassie,
The ecology and environment of the GI system is poorly understood.
Antibiotics can both cause the condition of IBS and potentially cure
it.
In Fall of 2007, I had an interesting experience. Due to
circumstances beyond my control, I had to take Augmentin, a common
antibiotic (Amoxicillin + one other drug) to prevent an infection (not
GI-related). It gave me diahrrea for a week or so, but then markedly
improved my IBS. This lasted around a month, but the effect gradually
tapered off.
Ironically, I blame Amoxicillin as one of the original triggers of my
IBS many years ago.
Most anything is possible!