Do they act constipated? Do they seem to hunch up and push and nothing happens, or are they acting normal? One thing I have learned from bottling babies is that they each have their own quirks. I had one boy one poop once a day, and it was the size of a dime -and he did this for the first month of his life -he seemed to be defying the laws of physics! He's probably over 2 months now, big and healthy, and poops regular pellets now. I had one girl who was constiptaed for several days, and then finally pooped out pellets and has been fine since.
If they do seem constipated, I know you can give enemas (you can use the kits they have for people). I haven't tried it myself, nor would it be my first course of action, but I heard from another deer farmer who bottle raises their deer that they use a 3cc syringe with just a drop of dish soap and warm water, and flush it into the colon (hold you finger over it to help keep the water in at first). Just as eating soap will give you the poops, it has the same effect in fawns apparently. I'd go with an enema kit first though before resorting to the soap method.