Your lemon is in a container? Mine is too. Actually, I have two in containers, the other had a bunch of flowers that budded into little tiny fruit, then all dropped off the plant about 5 months ago.
Yes. It has always been in a container. It is way past time that I should have transplanted it probably, but it’s in a pot about 13”x 13” x 15” tall, so I doubt that I could manage the change without harming it.
I read that when you transfer to a bigger pot, it should not be very much bigger to keep the branch growth under control. Also, pruning is supposed to help for some reason.
If your fruit dropped off, the tree may have been going into self protection mode and spending its energy to produce leaves for some reason. Maybe too dry, not enough sun, not enough nutrients etc.
Last time mine was dropping fruit, it was outdoors, and I gave it a dose of liquid nutrients, and sprinkled some slow release osmote type granuales around, and picked off all the rest of the tiny fruits except for about six or seven which was all I thought the tree could support. I kept picking off the flowers after they bloomed for quite a while.
When it is blooming and setting fruit, I usually use a liquid nutrient that is higher in phosphorus than the balanced types.
I have a lot of trouble with aphids during the summer months too.