My 4 1/2 yo daughter has SEVERE allergies since 6 weeks old. Our...

My 4 1/2 yo daughter has SEVERE allergies since 6 weeks old. Our specialist prescribed Zyrtec and she has been taking it every night for 3 1/2 years. We haven't noticed any obvious side effects as others have. She is certainly not drowsy (in fact the opposite!)A couple of times we have run out and she has missed it for 1-2 nights, and she has started itching ALL night. We have assumed that she needed the Zyrtec and rushed out and bought more. As I am getting concerned about the long term effects, started researching and found this site. Maybe we should consider that this was withdrawal symptoms and not the allergies. Does anyone know how long the withdrawals last? Thanks to all the posts for all the relevant information.