Can alcohol cause IBS? In a word, no.
Here's some further information on IBS from the Mayo Clinic.
Irritable bowel syndrome Causes - Mayo Clinic
What I *can* tell you, though, is that I'm pretty sure "bathroom issues" are universal among people with drinking problems. Without going into a lot of detail, I can tell you that things normalized for me in that department with sobriety. And very quickly. A healthy diet is important, too.