My lemon tree never blooms, what am I doing wrong?

probably the wrong fertilizer
Talk with a horticulturist as to what citrus trees prefer and the ph of the soil that they thrive in

Make sure that your Lemon Tree is well watered + fed with the appropriate food , when the flowers fall off they leave very small buds which may become the lemon, they take quite sometime to grow into lemons + because small you may think NO LEMONs - wait .

Just wait, sometimes it takes time for the lemon to grow. Take care, give time to time water and other necessaries to the plant.

this is bad -
see
http://www.sgaonline.org.au/citrus-gall-wasp/
had a lemon tree in Victoria it would have been 30 years old was starting to get this wasp. My brother in law lost a lemon tree from this as it sucks the goodness out of the lemons and the tree.

To treat, remove all infected leaves and dropped fruit from the ground. Prune the lower branches from the tree, those that are more than 2 feet from the ground. Then spray with a fungicide such as Agri-Fos orCaptan. Botrytis fungus - Botrytis rot is yet anotherfungal infection which may afflict lemon trees.10 Jan 2016

Lemon Tree Problems: Treating Common Lemon Tree Diseases

https://www.gardeningknowhow.com/edible/.../lemons/common-lemon-tree-diseases.ht.. What is the Treatment for diseases of lemon trees Google Search

tree is under stress from wrong soil PH, lack of water missing correct fertilizer, excessive water, wrong soil ( clay or other non water absorbing material
talk with a nursery professional and get advice

Lemon trees are extremely sensitive to over watering, only thing you can do is make sure you have good drainage. Dig channels at low points to make sure ground water moves away. Just a small point, you posted your question on the Cars & Trucks section, you may be missing some better solutions by posting here, however, I've raised a few lemon trees in Spain and in my front room in London so I have a little experience in this area.
Good luck