Thanks ladies. I did call the ped and we decided to start some cereal to hopefully thicken the bowl movements. In the meantime, she got a tooth! My friends told me that their babies had diaper rashes when they were teething. I called the ped again and she seemed to think that was it. She said something in their saliva changes when they teeth and for some babies, when they swallow it and it comes out the other end, it causes some irritation. The diaper rash is totally gone now that the tooth popped through!
The poos are still pretty liquidy, just the way it is with Alimentum, but they're not bothering her so I can live with that.
Mary