Is it IBS or SIBO?

Decades of bloating, stomachaches, pain and constipation led me to search for answers and find out what was really happening inside my gut.
In my twenties I remember the cleanse the night before to prep for barium x-rays. Afterwards I was given the typical diagnosis of IBS. This is assigned when the Doctors really have no answers, it refers to a collection of bowel symptoms.
In my thirties I remember having a sigmoidoscopy and they didn't sedate me. It was truly awful! Afterwards I had the worst gas pains. No new answers.
After a hysterectomy from a prolapse and endometriosis glued to my rectum, not only did my bladder freak out, but ... my old friend my stomach acted up again.
Can you relate to the stomach life? Not fun. I can tell story after story being out with family or friends having to find a bathroom. The good news in my search I found out I had a true casein allergy. When I stopped having cheese, my symptoms improved for awhile, because there were more chapters in my gut story to come.
How do you know if you have IBS or SIBO? And, what is SIBO exactly?
What are the most common symptoms of SIBO?