Stress can make any allergy more reactive. There's no simple answer for stress relief and it's highly individual. I can say that when I am able to reduce negative stress that a lot of my allergy symptoms go away.
I had a full body rash as a reaction to taking a medication just once. It took 6 months for it to go away. It can be really hard to know what you are / aren't doing is actually helping your rash or not. If you do have a systemic allergy, antihistimines do help and not all of them are the same. There's differences between sudafed, claritin, zytac. Allergies are a pain.