A creamy coloured discharge isn't normal and could mean a vaginal infection or worse, so should be checked by a vet. A bitch that isn't in season should not have any kind of discharge at all unless pregnant -and then the discharge is colourless. When she is abut to come into season, first she will swell a little in the vulva, then there will be a tiny amount of blood a day or so before she starts bleeding properly. The easiest way is to lightly dab her vulva with a white tissue each day, and see if it comes away red.