Red spots developed on shoulders and back after being in woods – Health & WellnessReport
Unless you came into contact with some type of poisonous plant, I would guess chiggers.
Only thing is, they usually find places that are rather restricted such as around your ankles or the waist band of your underware?
Do they itch, especially at night? If so, probably is chiggers.
They make a product called chigger-rid but clear nail polish would work too. You just put a drop on each red dot, this will cut off the air to the little critter and if it is chiggers, will provide you with relief and kill them.