good day.i have 4 acres of sweet lemon trees about 6/7 years old fully grown, 18 feet high with 12 to 15 feet girth.fully green .not apparently sick. not giving fruit or flowers except few. Few oranges planted by mistake in the same soil, under same conditions of watering/fertilisation are giving fruit. Sweet lemon plants drop lot of leaves and quite a few are lying next to stem. problem from Pakistan/ Punjab.
I would expect a nutritional deficiency. Do you have resources for soil testing and prescription mineral amendments based on actual deficiencies found?
Deep watering is important.
Affordable soil fertility building can be achieved with legume green manure inter cropping.
Mulching helps retain soil moisture content.
I don't know local conditions and citrus problems in the Bahawalpur region, I am located in Southeast Asia.
You may want to seek authoritative help from a local agricultural university extension program, or local crop advisor. Or seek friendly exchange with other local growers.