My doc prescribed me bulk forming fibre drinks over a year ago when my fissures were particularly troublesome... but they did not agree with me at all and made me very constipated & in lots of pain.
Found out this is because i have IBS & my body cannot tolerate wholegrain wheat.
What i found has really helped is eating lots and lots of oats!! Lots of fibre & my body doesnt mind oats. I say oats & drinking lots of water might be worth a try if you arent doing so well on the fibre drinks