What could cause extreme itchy rash in pubic area all of a sudden? Also have random spots on stomach, arms, legs, back and buttocks. No new detergent

Many. Contact allergy, bug bites, scabies- just to mention a few. If this has been going on for awhile, you should consult your doctor.
Itchy rashes. For skin rashes, a variety of skin conditions can present similarly with spotty itchy rashes. To get a correct diagnosis, we need to see and examine it so a correct course of treatment could be made. Spotty itchy rashes can be folliculitis, hives or eczema. They are treated differently. I would suggest you see a local physician.