Auditory Processing Disorder is one of the many things that is included in Sensory Processing Disorder. My DD1 has this as well as other sensory issues. We do a listening program, and attend OT. There are Paediatric Occupational Therapists who specialise in all sensory processing disorders and can do the assesments themselves.

I would go to your GP, but unfortunately a lot of GP's don't know alot of the advancements on SPD. I would suggest bringing in a bit of information regarding Auditory Processing and get that prior to going to your GP.