For me it was also problematic with any kind of oral iron because of my chronic inflammation. Back in colitis times I took the pills with the lowest iron amount, and even those made my bowel more irritated.
With chronic pouchitis I had high dosage infusions for many years about every 3 months. That way I got to normal iron blood levels. Since 2 years my need for additional iron has subsided, obvioulsy because I take antibiotics in regular intervals and inflammation is better under control.