What would cause a red rash behind both armpits? i just had an iud (paraguard) inserted on the 11th. could that cause this painful rash?

Local Irritation?: If it is symmetrical on both sides, think about local irritation from clothing or a bra. Have you used a new soap or perfume or other skin product with dye in it? Do you take any other medicines? I would not be suspicious of the IUD causing this kind of discrete rash.

No: There sis no association between the two.you may want to look at your droderant