Any other signs? White, milky discharge or maybe some morning sickness?
If it were me, I would figure a way to get an ultrasound done. If she is pregnant, you will need to prepare for that, so I would find out sooner than later.
Also, it could be a false pregnancy. If that is the case, I would let her finish this, then get her spayed about a month after.
Any chance you could post some pics of her standing, from the side. One of her standing, birds eye view and one of her laying down with pictures of her belly and nipples?