My German Shepard keeps having hair lost at the stomach and neck area below the mouth, any opinion?

Have you had the dog tested for Folicular mange.

This is caused by tiny mites that live under the skin and in mild cases just causes the hair follicles to die off, especially on the stomach.

These mites can lay dormant for many months before becoming active.

The application of Advocate in 2 three month intervals will usually kill off these mites.

My Gsd had hair loss on his stomach and tail and it was caused by this condition.

2 applications of Advocate cured it.

Severe cases though may be harder to eradicate

Chances are your dog has not got this, but its worth finding out?

Look up BRAGGS Apple Cider Vinegar, I give it to my dog everyday. It is number one in anti-fungal properties! It will help your dogs skin by ingesting it and by putting it on his fur! Also unrefined coconut oil and wild Alaskan fish oil will help. Feed him a tablespoon of organic plain yogurt too

Sounds like an autoimmune issue. Have you tried a consult with a specialist?