
You say she bled for two weeks, but the season lasts around 3 weeks, it is around about the time thae bleeding stops or lessens that the bitch is ready for mating. Was there anytime she was unsupervised for the 3 weeks or so after the bleeding started, and how long was she missing for, or did you see a neighbours dog in your garden?
It could be that she is having a phantome pregnancy, which to some degreee is normal after each season, as bitches undergo the same hormone changeds whether mated or not, but usually less dramatically if not preganant.
If you take her to the vet at 6 weeks after the start of bleeding, he may be able to feel for a pregnancy, or be able to scan her to make sure.
The vet may be able to spay her for you if she id found to be pregnant, taking away the pups with the uterus!