Lab won't stop licking leg!!!

[Lizzy]

For the last week my 4 year old Lab "Ghost" has been licking his front leg from his "armpit" to his "elbow" on the inside part. He is obsessive about it and just won't stop. It has reached the point that the whole area is now pink and the fur is getting thin. Took him to the vet 3 days ago and he gave him a "steroid-like" injection and thought it may be due to some kind of allergy. However, it doesn't seem to be helping. Does anyone have any idea what could be causing him to do this??? Why would an allergy cause him to just keep licking this one area??? Thanks for the help. I love my dog and want to help him before it gets any worse! Also, he does not have any fleas or ticks, as I use Frontline regularly.

[hillary]

Did the vet do a search for fleas ticks or other parasites?

That sounds like a possibility.

Hillary

[AZLS1]

It could be stress related. Is the dog alone more now than he has been in the past?