Certified GKH Gardening Expert
Lemon trees typically need to be about 4 years old to fruit. If yours is not yet 4 years old, I would give it a little more time.
If it is 4 years old and you are not seeing blossoms, it may be that the soil is lacking phosphorous. Have the soil tested at your local extension office. If you are seeing blossoms but you get no fruit, this is a pollination problem. You can hand pollinate with a small paintbrush. Just go from flower to flower and swirl the brush inside the blossoms.