[Ellie May]

I agree with Diana.
It could be either.

Is there any odd smell back there?
You can watch demos online and try to empty his anal glands but this is over done in Yorkies and may not be necessary in all cases of scooting.
Use your own judgment and when in doubt, talk to your vet, because you don't want to over-do but you don't want to under-do either because that can lead to impaction and infection.

If you see anything that looks like grains of rice on his butt, that is tapeworms. Scooting is a major symptoms. If you don't know what it is, take a stool sample to the vet.