Rylee had that issue too and still does a little bit, it started when we switched her formula..... the BM helped her a little bit she went from one poo in 48 hours to one poo in 24. We also tried water, but was told to be careful because its easy for them to choke on it.
I just took her off the BM though and its taking a few days but the single formula is working its way into her system and shes doing much better.
Her doc. said that it usually take 3-5 days for it to work its way in and even everything out. So maybe it just hasn't been long enough.
I really hope your LO gets to feeling better.... I know its hard to to hear them cry and not be able to help.
OH! our doc also told us to give her a 1/4 of a suppository... so you might want to ask your doctor about that it Really helped.