Omg I'm so sorry to hear that... I think you should go to the hospital just to make sure everything is fine
My OB has told my she has had many patients take a fall or slip on ice and fall on their buts and it's fine we don't realize how protected our babies are in there but if it was a really hard fall and your worried go get looked at for peace of mind but I'm sure you will be fine if it was just 3 stairs