Strange Diaper Rash in 19 month old

My daughter has these HORRIBLE rashes on her bottom.She will be fine and 1 hr later it will be so bad that she is bleeding. This began at about 1 yr of age when she was switched to milk. I began to avoid milk products and she would do fine. Slowly, it began happening again. This past January I took her to an allergist who diagnosed (scratch test) her with allergy to milk, casein, corn, tomato, carrots, bannana, apple, grapes.The doctor told me to avoid these foods and do food test. She has been doing much better but something just didn't seem right. I have found that she breaks out from other foods that I give her as well... It just seems like too many foods to be possible...Last week I took her to a different allergiest for a second opinion. He said that he does not think it is food allergies due to the location of the rash appearing by her bottom and how it appears 1-3 hours after she eats the suspected foods. He said it should appear almost immediately closer to her mouth or all over at once. He also felt that the list of foods were VERY rare to have such a reaction. He wants me to have the blood allergy test done. What is your opinion? Have you heard of children with this type of rash issue? Could it be digestive?