Hi there,
It must be really devastating to get the news you have. Hope you are feeling better. As SK says, azoospermia is a condition that can have many underlying causes. So the cause needs to be investigated and treated if possible - for example undescended testicles treated late and mumps can affect sperm production in men. Maybe your DH could ask his mum a few questions about childhood illnesses he may have had.
I really hope the next test shows better results.