Supposedly this is very common in IBS patients. I suggest the book, "A New IBS Solution" by Mark Pimentel. It talks only about bacteria overgrowth in IBS patients and how to deal with it.
According to the book you're suppose to take Xiafaxan(antibiotic) for 10 - 20 days. I'd ask your doctor if he's heard of this book as well since he's the doctor that came up with this discovery. Good luck.