|Hi Lisa -
Prickly heat maybe? This is a common sometimes itchy rash cause by sweat retention. Prickly heat (miliaria) is most common in the folds on the skin and where the clothing fits snugly. Treatment for this would be different than for allergic contact dermatitis (contact with poison ivy, oak, sumac). I am not a doctor and am only giving you some thoughts as to what this might be. Here are a few links with more information and treatment:
If you find this condition concerns you, you should talk to your doctor about exactly what it is and how to treat it.