Hi Marley,
He may be having problems with his anal sacs. These are located at the 4 o'clock and 8 o'clock positions of either side of the anus. Sometimes they get full and irritate the dog so the dog will constantly lick the area. He may also scoot along the floor to try and break them open. Normally these are expressed with a bowel movement, but if the stool is too soft, the sacs don't break. They can become infected as well. You may want to have the vet take a look if they are really bothering him.
Once they have been checked and the dog is back to normal you may want to talk to your vet about adding some canned pumpkin (not the pie filling) to the daily diet to keep the stool a bit firmer.
Here is more on the anal sacs. http://www.marvistavet.com/html/anal_sacs.html
dog training consultant
24 years training & behavior,pet first aide, Therapy dog eval., PA Animal Response Team