Thanks for the question.

While I cannot diagnose this via the internet I can tell you the following :

This could be as simple as fleas as the faeces of the flea do look very like little black dots. Sometimes the actual flea can be difficult to spot but if you part the fur and look carefully you will see them running about, above the dog's tail is a good place to look.

To confirm that these are indeed flea faeces you can comb some of the black dots from your dog's hair on to a piece of paper. Place one of these on to a bit of damp cotton wool and squeeze it, you will see a red halo which is from dried blood in the faeces. { fleas suck blood you see }

If it turns out that these are flea faeces the first thing to do is to treat your dog with a good flea product such as Frontline and also treat the house with a spray as well as there will be fleas in the house and in the carpets as well as her bedding. If that fails to resolve your problem or if things get worse you should have a vet check your dog over.

If I have not covered your question fully enough or you would like to ask more I will be online for the next hour or so and I will be at your disposal.

Scott Nimmo BVMS MRCVS