My son has never slept a full night due to side effects of medications.

Patient: My 4yr old son takes 4mg singular chewable tablets and 5mg zyrtec chewable tablets everyday it causes him to have extremely dry mouth especially during the night. He’s been taking both medications since he was 18 months and I have tried anything anyone has suggested. He has never slept a full night he gets up bout average every 2-3 hours wanting water. What can I do please help.