After checking tail, tailpocket and butt area? This happened to us for the first time with Onslow and I had a feeling he needed his anal glands expressed. Yes he did! If you are experiencing this (even if your dog has never done it before) it could be an anal gland issue. The vet can do it.
Just posting to maybe help someone else! He feels much better now but YUCK I wouldn't advise doing it at home. LOL

100% right! Mason does that
100% right! Mason does that too when it's time for him to have that done. Once it's done, he's fine!! Do it myself?? I can't even be in the same room at the vet when they do it!! Yikes!!!
I witnessed it :(
oh it was unpleasant.
Our Vet called it 'Dragging bottom'
Does your dog 'walk' on its front legs, while 'scooching' its butt across the carpet? if it does . . . Anal Glands
...
Our 1st puppy was a lab (Tori) she had issues and when she got groomed they took care of it - it is nasty, and I only recommend it for the experienced (atleast strong stomached!) but gosh does it feel soooo good for them.
We've had Gizmo checked, and she went through it, and her glands were fine (Poor Gizmo, has had so many Tail issues, that she HATES going into the Vet when that rubber glove goes on ! !)
Last steps taken May 26, 2014 -- Been rolling along ever since . . . .