scratching and odor

Question
I have a 9yr old yellow lab (male), he constantly scratches behind his front shoulders, the areas do not appear to be irritated,scratched ,bleeding or scabbed.I was wondering if it could be nerves I have heard of hot spots in dogs or is it a skin condition.
I also noticed that he has developed a stronger than usual doggie smell , could this be oily skin/fur due to his new brand of dry dog food as I  changed it a little while ago as well as now adding a little canned food to his dry stuff.
Any advice or information would be greatly appreciated...lawrie  

Answer
If this happenned after a diet change, then I would suggest going back to the previous food.  If it is an allergy, then your vet may be able to give the dog a shot to relieve the itching.  I often recommend dipping itchy dogs with an insecticide that will kill sarcpotic mites, even though you don't see any bugs on the dog.