Hi, I had gone through your question and understand your concerns. You should be worried but not too much. The most common side effects of Cetirizine: drowsiness; dry mouth; stomach pain; tiredness; trouble sleeping. Seek doctor s attention right away if any of these side effects occur: Severe allergic reactions (rash; hives; itching; difficulty breathing; tightness in the chest; swelling of the mouth, face, lips, or tongue; unusual hoarseness); dark urine; fainting; fast or irregular heartbeat; mental or mood changes; persistent fatigue; seizures; severe dizziness; unusual bruising or bleeding; yellowing of eyes or skin. Sometimes allergy to antihistamines occurs,if you saw swollen gums after zincet, then don t give,change medicine. Please let me know if you have further questions before meeting your primary care Doctor.