Can a middle ear infection and fluid in the ear cause irritability? and will zyrtec drain the fluid in the ear?

Yes/no: A middle ear infection can cause discomfort & irritability. There must be fluid retained in the middle ear space for an infection to occur. It will drain down the Eustachian tube on its own timetable. Antihistamines can thicken the fluid & delay drainage but might help when there is an allergic component. I never use them for this.