Why are my fig tree leaves yellowing?

https://i.imgur.com/OmjDG8i.jpg

I planted this fig tree a couple of months ago and although at first the leaves looked good, the new ones have been increasingly more yellowed. I water it once a week, about five gallons at a time, a couple of times if the weather is above 90 during the day for several days. It grows in pretty much full sun (until probably about 5pm during the summer). I am in zone 8B.

I realize the photo makes it look like there is grass underneath it, but that's just clippings, I've kept the area around it pretty clear of grass, there is a border and I also weed regularly.

The soil around it is pretty heavy clay, but we filled in better soil in a hole around 18 inches diameter and probably 2 feet deep, mixed with some of all this stuff: http://i.imgur.com/0PtlOQz.jpg