It looks similar to an eczema rash I get, so check out al eczema sites online that have photos that look your your style rash. Search for eczema rash photos. Eczema has a dozen different forms.
My torso rash, a form of eczema less common and has specific commonalities and is called Grover's Disease or Transient Acantholytic. Dermatosis, TAD. It is specific to the torso area front which includes the abdomen and back torso and normally doesn't leave the trunk area, but for some can progress down arms or up neck. Most with it have a form of leukemia, lymphoma or other autoimmune disease, another form of eczema, have had a recent hospital stay of about a week which required bed rest afterwards, have abused their skin spending too much time in the sun, are mature adults and I had all these criteria. The only one I didn't meet was that more men have it than women. My first outbreak lasted 1 year which is normal, but have had 2 subsequent recurrences which lasted 6 months each and each time the outbreak is less severe. It is not triggered by contact allergies, but by heat, sweat and friction.
Something is causing your rash, my 4 forms of eczema have overlapping symptoms (rash) and all manifest if unique ways also. I sure would explore the eczema possibility.