The only way to diagnose allergies is to see an allergist. These doctors are specialists in their field and use different tests to figure out what you are allergic to. These tests are either via skin tests or blood tests.
The skin test is a simple test. The allergist will perform this test on either you back or forearm. They will place a small amount of the allergen on your skin before pricking the skin. This is a very accurate test with results available almost immediately.
Blood test take longer because once the Doctor or Nurse has drawn the blood, it is sent to a laboratory for testing.
It could take 2 or more weeks before results are obtained.