My mom, aged 72, has cyclical symptoms that occur every 2 months: chills, fever, body aches, vomiting. Blood work, other tests all come up normal?

Cyclical disease. I would want to know if it was exactly 2 months at a time -and for how long she was experiencing this. There is something called cyclical neutropenia, but it's very rare. I think she needs to be evaluated when she's actually sick -because when in recovery you may not identify the cause. I think your mom needs a thorough evaluation - and it may be time for that second opinion to shed light on this.