My cat hasnt pooped in three Days! Help please.?

Me and my friends recently saved two new born kittens. They are about five days old now. The little boy has pooped several times since we have had him. But the little girl has only gone once. It took her two days for her to poop the last time. But we are going on day four now and I have done every thing I can to get her to go. We have wiped her bottom. The thing is, is she eats a ton and pees all the time. But her tummy seems to be very bloated. We are also bottle feeding her and I don't know if that has anything to do with it. There mommy had abandoned them. I don't know whether to take her to the vet or what. Is there something I can give her to make her go! I need some suggestions please. I don't know what else to do. I am getting very worried:(