What is the cause of snoring I don't snore before my weight is increased all so I gain 20 kg?

Snoring with weight. Agree with dr holt. Talk to your doctor as you are losing weight. You have a risk of sleep apnea and it needs to be ruled out as soon as possible. If your sleep study is positive for sleep apnea, treatment with CPAP of other therapy in addition to a focused weight loss plan become imperative.
It's the weight. When you gain weight you also gain fat tissue in the back of the throat. This contributes to the narrowing of the air passage and it collapses when it relaxes back there during sleep and the tissue vibrates and causes the audible snoring. If it's bad enough you'll have episodes where you stop breathing. This is called sleep apnea and can be dangerous. Lose the weight and talk to your doctor.
Vibration in throat. Snoring is caused by vibration of the throat when you are sleeping. Many times, the throat narrows at night when the muscles keeping the throat open relax with sleep. It is very common to snore with weight gain, because there is more tissue in the throat that causes more resistance to breathing at night. Snoring may be a sign of sleep apnea, which shouldn't go untreated.