Chilean Mesquite losing leaves
about a month ago, i purchased a chilean mesquite from home depot. i planted it and set it up on my irrigation system with a 2 gallon per hour head for 8 minutes twice a day because my soil, here in yuma, is just sand and pretty quick draining. about 2 weeks later, the tree started to lose leaves and i discovered that the sprinkler head was leaking and the tree was getting about 5-10 gallons per hour. i then capped the sprinkler to allow it to dry and have even put garbage bags around its base to keep any sprinkler over spray form the grass off of the tree. much to my dismay, it still hasnt regrown its leaves or started to grow. it has a very frail and weak look to it and i was wondering if maybe it was just a combination of the shock from too much water and it being winter that has restricted its growth or if it might be sick. i have read that these trees are extremely fast growers so i am worried about mine not growing at all. maybe it will thrive in summer when the temperature is hotter and drier?
any help is greatly appreciated, i would just like for my little tree to look healthy again.