The leaves could be mechanical damaged or a pests that eat during the night

I have never planted a tree down there but up here it takes at least 3 months or more before any tree show growth while it adapts..Give it time)

Are you fertilizing it and with what? You should have great growth soon living there.

Looks wind whipped - maybe from riding in a pickup truck on the freeway too long. It should come out of that once the roots get happier.

Since you live in CA, I am sure your gardener could have found you a better looking tree or treated it with much more care. Costco sells citrus trees from what I have read. At this time of year, your temps are still cool. Give it a few more months. Hopefully by July, you will see some new growth. If still nothing, then the soil needs to be examined. California has a lot of clay based soil so it is possible the drainage is not good.

It also seems to be buried just a little too deep. It's hard to say how deep it is, because I can't see the roots at the base. Should be able to see the roots.

Also I would untie all those green ties up the stake and replace them with something much more loose. The tree needs to be able to flex some to grow a sturdy trunk.

And finally, it is at least 4 feet too close to that fence. A lemon tree will grow a canopy that is 10 feet (or more) across.

I would remove that supporting stake completely unless that spot is very windy, which would make it not ideal for a citrus tree anyways...