See an allergist. Both kids and adults may have positive blood tests to things that don't cause an allergic reaction, and some things that do cause allergy symptoms may not show up on a blood test. The best way to diagnose allergies is to consult an allergist who will do skin testing and then interpret the results in the context of your child's symptoms and exposures. It's more complicated than a simple blood test.
See an allergist. Probably the best way to approach this is to see a good allergist/immunologist, who specializes in this field. They can look at the allergies your child has and determine therapy, as well as what foods and products to avoid so as not to trigger an allergic reaction. They can also find out how sensitive your child is to some triggers and prescribe items like Epipen (epinephrine) for beestings to stop it early.