Dear friend,
It is very rare to get allergy only in one eye..
You might be having anyother problem in your left eye..
Possibilities are
Probably foreign body or eye lid gland inflammation or possibly any other problem.
Its better to consult eye doctor near you..
Depending on your history only so much can I help you ,further can only be confirmed only after examining in person.
All the best..
Next Steps
consult eye doctor near you..
Health Tips
it's already been one week you are suffring from eye problem.,
no point in waiting further..
better fix an appointment with your eye doctor near you.