Hi, my dog is 13 year old pomeranian. Lately she been walking slowl and get tired after couple of steps. Also I notice that her stommy get bigger.what could be wrong with her? Thank for answering my question.

She could be suffering from arthritis. I would take her in for a checkup and they will be able to help you.

13 is getting old for a dog of any breed.
There could be quite a few things going on with her.

Only a vet will be able to tell you for sure but as Sariss said arthritis is very common in older dogs and can definitely slow them down.

The larger stomach could be anything from being overweight to worms to gas.