Patrick,

With regard to your first question, I couldn't say why your polygrapher would have said you were lying about your date of birth or your citizenship. If you were administered a Relevant/Irrelevant polygraph interrogation, then, if these questions were used as irrelevant questions, your polygrapher might have actually been attempting to help you pass by sensitizing you to these questions, rather than the relevant questions. What were the questions that you "exaggerated" about? For further reading on polygraph procedure, see Chapter 3 of The Lie Behind the Lie Detector.

With regard to Claritin, I am not aware that any research has ever been published about its possible effects on a polygraph interrogation. The website DrugDigest.org lists the following side effects for Claritin:
 

Side Effect	Incidence for Claritin (%)
stomach pain	2.0
drowsiness	2.0
dry mouth	1.0
fatigue	1.0
headache	1.0
stomach pain	2.0
general ill feeling	2.0
nervousness	2.0
wheezing	2.0