Possibly a dietary thing. What are you feeding your dog? Adding a good supplement and vitamin to the food might fix the problem.
Is your dog is eating grass outside? The dog could be suffering from a gastric upset and try to make himself trow up. If that's the case, don't let him do it and talk too your vet?
Excessive licking is often related to stress.
Some dogs are more sensitive and stress easier than other (just like for human) and will look for a way to release the tension.
More mental or/and physic stimulation might help.
When you catch the dog licking the floor,you could give him a peanut butter stuff kong or a puzzle stuffed toy like hide-a-squirrel. Those are great mental stimulation. You can also teach the dog new tricks or play retrieved the ball.
And last but not least . A daily walk usually do miracle...
