Pregnant Pitbull acting weird- no labor. ?

So I got a really small pitbull female on craigslist 4 months ago and was surprised to see her go into heat. I decided to breeder to my neighbors pit since he is really muscular and big. He said she should have gave birth already from the time we put them together. I don't have money to go to the vet so I wanted to know if Tgere is something to look for to know she is going into labor. It's our first breeding so we really dint know what to look for. She isn't herself though and is walking Hella slow lately, lol. Looks like she is creeping. Anyone, please help.