What's wrong with my orange tree? [9B]

My wife and I inherited this orange tree along with our house about a year ago. It has struggled since day 1. It produces very large oranges (think large grapefruit sized) but they are not juicy and somewhat bitter. My wife refers to them as dry. A good portion of the leaves are curling and discolored. They are always like this, not just at certain times of the year. I was wondering if this tree might be diseased in some way or just improperly watered.

We have given it a deep soaks inconsistently it but haven't been that great about it, to be honest. Is there something else wrong with our tree besides my thus poor watering habits? Your help is appreciated. We are in southern Arizona in zone 9B.

Here are some pics for reference.

http://imgur.com/a/lMyMg