It is difficult to get oranges to fruit when left indoors all year. Have you tried to give a dose of high nitrogen fertilizer? Usually fertilizing stimilates a citrus tree to bloom. Oranges usually prefer cool nights, which it isn't getting if left indoors all year. Try putting it outside on a patio in late spring through early fall after all danger of frost is over. Be aware that if the temperature and humidity outside it is very different than inside, the tree may go through shock when moved between the two. As for the leaf drop, it is not normal. One of my valencias lost leaves like that last summer. It turned out to be underwatering. Once I increased the watering schedule, the leave drop stopped.

If the tree is otherwise happy, I wouldn't worry about it too much, but it sounds like it needs fertilizer. I use the granular fertilizers they sell at Home Depot and Lowe's, follow the directions on the package and my trees in Point Loma are very happy. The EB Stone organics they sell at Armstrong work well for immature plants, but become cost prohibitive when the trees are mature.

With the size hole you made and the soil you filled it with, what you have done is created a "clay pot" the size of that hole; but a "pot" that has no drainage. Your roots will simply fill up the new "pot" and then stop growing; the stark difference between the mix in the hole and the surrounding clay in terms of pH, density, etc. will never encourage the roots to grow into the clay. If it were mine, I would dig it up, make a hole at least 2 feet deep and two feet wider than the dripline of the tree. Backfill that with a mix of your soil amendment with the native clay (1/3 amendment and 2/3 clay); that will give you a better shot at success. I would certainly do the drain test described above; and if the drainage is poor or non-existent, you might have to make the hole significantly larger.

I think you have two problems. First, the "greenhouses"; by putting them over the tree, you are changing the light, the temperature and the humidity; the tree responds by dropping leaves and replacing them with leaves more suited to the new environment; this is not unlike if you moved the tree indoors, as in potted plants. In Sacramento I would only put the covers on the trees, if the temperature will be below 30; and then I would take them off as soon as the temp. rises above that. Second, judging from the white/dead spots under the tree, I would guess your dog likes to pee on your tree; while it is arguable about the benefits of humans peeing on citrus, dog urine is very strong and can damage a small tree.