I saw my GI and he said that fiber powders were not very helpful and I should take Metamucil wafers (each pack has two cracker size wafers that taste okay). Within hours of taking them, my stool was bulked up and has been since.
For anyone having liquid stools, I definitely recommend trying Metamucil wafers (if your doctor says you can have fiber and your loose stools are part of the normal recovery and not another problem).