Hi i have no medical experience but i can tell you what i have experienced.As Screamer said Benefibre should be fine if you start off slowly and build up.as for pelvic and back pain, i was suffering this quite badly and often without tummy pains, i went to my gastro and he said the pain is likely due to the many nerve endings that attach from the muscles in your gut to the back and side pelvic regions...So basically it is all linked to IBS he thinks