This deserves it's own thread to describe how complicated this problem is, and how poorly understood it is.
Urban IPM Extension people can go through samples to find insects, inspect homes for infestations (bed bugs, fleas, etc), get someone to do skin scrapings for Scabies, etc.
Often times, attempts at self-treatment can cause skin irritation. Pesticide poisoning can also cause crawling sensations.
Brain tumors, autoimmune diseases, even cold weather can do this as well.
en.wikipedia.org/wiki/Sick_buil…
There's really no way to know for any specific case, and entomologists can't diagnose most of the causes of Eckbom's symptoms.
It's an incredibly complicated web.