Obvious question so excuse it please ,but did you get the dog as a pupy or an adult? . If it was the latter it might have been spayed before you bought it .
The best bitch I owned used to have a season only every 18 months or so and even then absolutely refused to be mated . She lived a long happy life and was still coming ferreting at 16 so I would'nt worry too much as long as your dog is otherwise healthy .
i got her from a pup off someone on this site shes a cracking bitch with no other problems.i dont know if i can say who bred the bitch