If she is not spayed, and you are completely certain she is not pregnant, then this is likely a false pregnancy. This can occur in dogs where the hormones act like she is pregnant without the presence of puppies. The signs include nipple and vulvar enlargment. Milk production, nesting etc are also signs of this issue. Most of the time, it will resolve on its own. In some cases, your vet can use a medication to bring her out of this, but it may not be necessary. Either way, over the next few months after she comes out of this watch for signs of increased water consumption and lethargy. If you see this, this could be an infected uterus (pyometra) and she should be seen. Just a heads up, I don't expect an issue. I hope this helps and gives you direction.
Thanks, XXXXX XXXXX just worried. She never acts that way, and there is a white milky substance coming from her nipples. She is not spayed. I was afraid it may be an infection of some sort. If she were in pain, would it effect her running around and such. That does not seem to be a problem?
Probably not an infection, but if one of the nipples gets hard and swollen mastitis is a concern, but I rarely see this with a false pregnancy. Sounds pretty classic. If she still is showing signs in a couple weeks, call your vet. I hope this helps.