I have a Meyer's lemon tree that is several years old and this year it has flowered, I pollinated because we don't have many bees, the fruit has set but I am finding that quite a few of the baby lemons are turning yellow and falling off the tree. Any idea why this would be happening?
The tree will drop what it can't support. So, it needs sunlight, nutrients, and water to make fruit to surround seeds to make more lemon trees (from its perspective) and will either reduce fruit load to match inputs available, or give up on fruit entirely in the hopes that it can survive to next year and try again.
If it's only "several years old" it may not be able to support many fruit even with adequate resources available, as it may not be large enough.