It could be endometriosis. Many women with endo also have IBS and, unfortunately, mistaken diagnoses are common. I was told for years that all my ab pain was from the endo, actually, I was told for many more years before that that all my ab pain was normal. Rectal bleeding during your cycle is a symptom of endo. I suggest you do some research, many doctors claim to be endo specialists but aren't.
After suddenly developing anemia unrelated to my cycles, they decided to take my complaints seriously. A few months ago a pill cam showed that I had ileitis.
I hate when doctors get lazy and blame all your symptoms on a previously diagnosed condition, they don't want to bother checking for other causes.