So, I have hives, also known as chronic urticaria. Basically, I break out when the climate I am in is hot, or when I exercise. I visited my family doctor and he told me to get a blood test he also gave me a Cetirizine (Zyrtec) prescription which is 20 mg. I have been taking this medication for about four days now, and I still get these itchy hives. If I were to get a blood test, will the doctor be able to prescribe the right medication, so I can get rid of these annoying hives?