Can you help me identify the source  of bites on my torso only, that
are persistent and cause infected open wounds, that takes weeks to
heal and leave scars?

Background: Within the last year, I have started to
experience occasional bites on my torso only, from neck to pelvis,
front and now back, some of which generate a local apparently allergic
reaction that results in a large open nickel-sized wound and infection
that takes weeks to heal and leaves scars. Smaller uninfected bites
are small red bumps that never occur on my ankles
or legs. Sometimes there is also a more generalized bumpy-rash like
effect, which may or may not be related.  The bites do not happen
daily and they do not itch. I do not feel myself being bitten.  I
alternate in my theories as to where I might be getting exposed...-- I
sleep in pajamas now; I have not owned a pet for over six years and
when I did I never had this sort of reaction to a flea bite.  I have
read and see none of the evidence suggested as common for bed bugs. I
don't see a lot of spiders nor any dead spiders in the bed. I have
shopped at thrift stores, but if I buy any clothing, I wash it. 
Dermatogolists can't identify the source of the bite. But they say it
appears to be an insect bite, though at times, I wonder if it is
something more of an internal eruption.  Prior allergy testing did not
suggest I was allergic to mites. Even with topical medicines, the
infections still come.  I can't understand why this has suddenly
started and persists.  Other data: the mattress, which I've had for
five years, has a padded top with cashmere in it.  I wash bedding in
hot water every week.  I do have a down comforter that I've had for a
long time, but I removed it and also flea-bombed the apartment and was bitten
afterwards anyway.  I would love to know the source of the bites so I
could protect myself. I can't figure this out or how to go about
getting to the source of the problem and eradicating it. Thank you.

Do you dry your laundry outside?  Also do you share your washing
machine(s) and dryer(s) with anyone else.  Depending on the area you
live in there may be many culprits to blame for you wounds.  Being an
archaeologist I have been exposed to many creepy crawlers and have
taking up a hobby of identifying them whenever I go out into the field
for research.

I will check back for more info.

From the facts that the bites occur occasionally, at night, and in one
general area of your body, I'd say bedbugs. You don't need many to be
bitten - and if there's only a few, it's difficult to work out what's
going on. But that doesn't fit with the bites not itching :-/
Residual insecticide seems to do the trick, generally. But you might
want to speak to a professional about that.

fleas