I Suddenly Started Itching All Over Without Any Rash. It

I suddenly started itching all over without any rash. It started about two hours ago after I was outside in the shaded heat and humidity for about five minutes. I do break out in a rash if I'm in the heat for too long, but not in five minutes. I only take 81 mg aspirin and 5 mg zolpidem at night. I do have several allergies and am highly sensitive to poison oak and ivy, but I've had no contact with those plants. The only thing different is I soaked in Epsom salts this morning.