acacia fiber with gastric bypass??

has anyone tried the Acacia fiber after gastric bypass???

My dr wants me to use citrical powder but i am leary of it.  I am 2 1/2 years out.  I'm afraid the acacia fiber will make my stomach get bigger when it expands after taking.  I have IBS and right now i take Amitiza but my primary care dr does not like.

Tamara