The source below my help you diagnose your rash.

They have come out with a wonderful itch relief gel from Benadryl I recommend. If it is poison ivy or allergic reaction or even a mosquito bite, as soon as you put this stuff on, you get relief

More than likely you got yourself into some poison Oak or Ivy, stop scratching or you will spread it to other parts of your body.
Use some Caladryl Clear Lotion ( not the pink one it looks funny on your face and neck ) and use Lanacan Antiseptic these will help with the itch and help prevent getting infection from scratching.

Sounds like contact dermatitis from exposure to sawdust and other irritant particles. Could also be a photosensitivity reaction if a medication or topical lotion used. Cortisone cream and a few days should help. If not try claritin otc. If not that then see your doc to get on some prednisone-if your not diabetic. Good luck.

It is what is known as prickly heat and happens along with sun burn. It is best to wash with very mild medicated detergent and then put on lactocalmine or a medicated powder which ever you can find at your pharmacy.Takes a few days to settle down