Please take her to the vet for a physical exam, and get her full bloodwork done. If that all turns up nothing -then maybe the problem is behavioural.
Dogs can have behaviour changes when they are unwell. Of course they can't speak English and tell you they feel a bit weird. That sort of thing can happen when they are not ill enough to be unable to get off their bed, or crying out in pain. But maybe she is trying to convey to you she doesn't feel too great.
It is also possible it is hormonal, if she delivered pups two months ago. I am sorry to hear the pups didn't make it.
I would also ask your vet about the chance she could have Pyometra...(?)
I don't know what the chances are of her delivering a healthy litter in future. But it might be wise to consider having her spayed, if she is physically fit enough. The bloodwork and physical exam should show if she is, or not.
Pyometra in an unspayed female is very common in later years. It can quite often be life threatening and a medical emergency, and sometimes the symptoms of its onset are subtle. With that, a dog can die in a matter of hours, while their owners think they just have a bit of a tummy upset.
I hope she is okay.
If the vet can't find anything physically wrong, then the problem is behavioural. The best plan is to follow the advice of a good behaviourist who works with positive reinforcement. You may find someone local....you may be able to research that online, or speak to someone online, and apply the method yourself....or your vet may be able to recommend someone.