I've been breaking out with hives all over my body neck chest arms legs and thighs mainly on thighs the most but all over my body why is that?

Allergic reaction. You are having a generalized allergic reaction. Hives can occur anywhere on the body. Many things can trigger an allergic reaction, certain foods, medication, insect bites are the most common causes. I suggest you seek immediate medical treatment.
Allergy. This is likely an allergy to something. Could be a medication, a food, or something in the air such as mold or pollen.. Take Benadryl (diphenhydramine) or Zyrtec to help itching. If no better in a day or 2, we your doctor. If you develop trouble swallowing or breathing, go to Emergency Room. Good luck!