What Causes Swollen Itchy Welts On My Neck And Waist?

Hi. I have been doing a juicing detox for about 6 days now. I juice with fruits and veggies that ive always ate, for the past 4 days I have been getting swollen itchy welts (similar to mosquito bites) but there different shapes and sizes around my neck and a few random places from my waist up. Everytime ive got these itchy welter ive taken benadryl and its helpped. Ive played around with it and did just all fruit one day and then did all veggies the other to see which one caused it and they still appeared both times. is this just something that will eventually stop because its toxins from my body or is it an allergic reaction to something? I don't want to stop juicing because its so healthy and I love it! Please help!