well you should start noticing her thickening up in her waist line about four to five weeks in. The last two weeks to ten days she does gain her most weight as the pups themselves are getting bigger and prepared for delivery. Then right before birth, they will 'drop' and you will almost wonder if she looks smaller lol but they have just moved down and back into position. But ya she probally wont express milk from her nipples her first litter until right before the pups are born, mothers who had a litter before may start expressing milk some days before. Did you mark down the date that she tied on? There are always the chance of false pregnancies which can mimick the real thing even up to the end.