Mites
I thought I had some type of bug when I was first diagnosed with Rheumatiod Arthritis. I went to my Priimary Care Dr. who did not investigate my complaint of itching and rash but gave me a RX for lice. This went on for almost 8 mo til I learned more about RA and found out I can have itching and rashes. It didn't go away from all the Dr. treatments and drove me up a wall. I even went to my local extension service and hd everything I brought looked at. Nothing was there. I washed everything, shampooed, vaccuumed etc. Exterminators said I coul be allegeric to something. When I read more abut RA and talked wit my specialist, I then learned it was from the disease and learned to calm down whenever I felt that way. One thing for me is when I would scratch the itch, it would hurt instead of releiving it. I got rid of that Primary Care Dr. as she did not understand RA nor did anything but write scripts. So she had reinforced my fears of having bugs.
Take a sample of your fabric to your extension service to look at under a microscope to see if it has mites and treat accordingly to their advice.