Benefibrer, Fybogel, vit C all those things work for me. I suffered pre-op with IBS so I was already a Benefiber user and I think that it has helped. And the water really helps, I can tell when my water is too low because I get constipated and get a headache! As a matter of course you do need dietary fiber so make sure you either eat enough daily or take a supplement or in your case maybe both while you are constipated.
Hope you feel better soon.