The guilt you are feeling is not irrational, as you have nothing to feel guilty about; however, I know that you have probably been told this time and time again by friends and family. So I know that telling you that probably won't help anything. I'm sure that this relates to some deep psychological trauma. SOMETHING happened in your past that was not in any way your fault, but that you blame yourself for. I'm sure that it must have been something quite traumatic. Its probably manifesting itself in this irrational feeling of guilt that you experience. This is something that would best be worked out with a professional therapist.