I have pruritus ani. Can I have soy milk or any other foods that I'm not allergic to?

Define "allergic" Blood or skin tests that are not reactive to soy or foods do not mean you can ignore them as a problem. You may be intolerant to them. You need to use that information as a guide but add a food diary using elimination to decide if an item aggravates any particular symptom.
Food allergy. Food allergy is defined by a reprodicible symptom that occurs after eating it; if any food seems to cause repeated symptoms, avoidance is the only answer. The presence of allergic antibody (ige) to a food, noted by blood testiing or skin testing alone does not prove allergy.