I lost about 12kg in 3.5 months (diet and gym) i stopped diet(only gym) but i still losing weight(1kg in 4 days) is that normal how to keep my weight?

My first thought: is that the dietary changes you followed to lose the 12 kg have become habits now and you are unconsciously following them in your daily eating. Do an inventory; make sure you are consuming at least 2000 kcal daily (probably more!) of healthy, balanced nutrition. You might experiment with cutting back a little on exercise and see if your weight stabilizes. If still losing, need to see your Doctor