My left eye is teary and sometimes itchy. what could be wrong?

Several things: This is a problem that necessitates a face-to-face meeting with your doctor. This will allow him/her to examine you, ask specific questions. And possibly order tests to find out what's wrong and what to do to help you.

Allergies: Your description sounds like allergies. Try cool compresses, artificial tears, and topical and/or oral allergy meds. If no improvement, see an eye doctor.