Firstly go to the vet for a check up - dogs cannot express when they are unwell or in pain and this can change their behaviour (personally I'm a grump when I'm sick or in pain dogs aren't much different). Then if you get the all clear healthwise DO see a behaviourist ASAP. Please don't try and self diagnose the underlying issue and try to fix it with some "miracle" training program you have found on the internet, a professional needs to come and observe the dog themselves.
Here are a few links I found I am hoping they will be useful to you.
this one is advice on what to look for in a trainer:
http://www.inch.com/~dogs/tips.html
this one has a behaviorist directory:
http://www.certifiedanimalbehaviorist.com/