If you recently moved to a new area, it could be allergies to something in your environment. If an apartment, did the previous owners have pets (cat / dog / bird)? Maybe change the air conditioning filters and install hepa filters?

If you visit an allergy doctor, they can give you an allergen test to determine what exposures might cause a rash. It might be something simple, like you live downwind from a neighbor house, vacant lot or business that is the source of your allergies.