Q.What Is Wrong With My Lemon Tree & How Can I Treat It?
Please, see pictures & help me treat my tree. Thanks!

Certified GKH Gardening Expert
It may be a pH imbalance. That, or the soil may be too compact to suit the tree. This can appear as deficiency and pH imbalances, since it will cause the same issues by suffocating roots.
There are a few things that you should test. These articles will help:
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/testing-moisture-in-plants.htm
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/testing-soil.htm
https://www.gardeningknowhow.com/garden-how-to/soil-fertilizers/soil-ph-plants.htm
Your local extension can help, as well: