Her nipples nearest her back end will become much bigger, they will both widen out and grow in size, they all will, but these will be the most noticable.
Mine had 11 pups each and they were huge in size from 5 weeks onwards and they also lacked energy when walking, even Phoebe who's a real live wire. Penny's appetite remained good throughout her pregnancy but she did have "morning sickness" and did go off food temporarily around 3 weeks after mating. Phoebe's appetite took a real nose dive and she was also sick. I struggled to get her to eat anything throughout her pregnancy from 3 weeks onwards.
A friends dog was also mated around the same time, this one had had 2 or 3 failed matings beforehand and the stud dog owner had basically told him if it didn't work this time get her speyed. She had 10 pups and her activity levels remained high throughout her pregnancy (she is a working springer), she was able to do a lot more than mine. The same owner on a previous mating was convinced she was pregnant as she seemed to do all the things you'd expect to happen, even getting bigger. He took her to the vets at 9 weeks only to be told there wasn't a pregnancy.