Do you think my dog is pregnant?

I thought my dog was at the end of her cycle. She is not spayed. We recently got a puppy, he is now 5 months old, we have had him for a month now. He is due to be fixed next month. He was trying to mount my female about 1 1/2 weeks ago but recently stopped. They did not mount together (As what I saw). I called the vet to ask if he could get her pregnant and he says he doubts it. Now this is what I am wondering. About three days ago my dogs bottom nipples started to swell, shes taking toys and making a nest, she is lactacting alittle bit, and whining (at everything but not a painful wine). More like a I dont know what to do with myself whine. I called the vet again and he said its more than likely a false labor and that I should put a warm cloth on her nipples that it will pass in about a week, if it doesnt to bring her in. What does everyone think? Does a dog show pregnancy symptoms this early? Do you think it a false labor? Also, some ppl said that you will know if he gets her pregnant because they will stick together but they didnt do that.