The skin rash begins with a small reddish mark, maybe similar to something caused by an insect byte (not likely the cause). The itch continues for several weeks and then it disappears, but the mark remains though more soft. Those marks, with distinct time-span, are located in several parts of the body.

My wife uses chickweed ointment and it does alleviate a bit. She doesn't want to go to the doctor yet, as they usually prescribe cortisone or antibiotics.

We went out of town for about a week and the itch was gone during that period, only the skin marks were still visible. After our return, it all started again.

Stress… allergy? We don’t know what’s causing the rash.
I’m posting some actual pics. Any recommendations concerning the best course of action/treatment are welcome. Thanks!

Actually that does look like an insect bite to me.  The reason is the quick growth over the hours.  If it were some type of contact rash then it would be sudden over all exposed areas, not starting small and growing.  

You can apply licorice root tea topically for a steroidal anti-inflammatory.  Internally, this is one of the few times I would recommend ginger.  Take this on an empty stomach as long before meals as possible.  The enzymes in ginger can help break down proteins in venom.  Either myrrh gum or echinacea tinctures can be used to prevent any tissue destruction or spread of a venom if present.