I'm burping frequently while going to bed so, while at bed i feel nausea which makes me feel like suffocating little bit. i gained 25 kg so, is it due to acidity or gastric problem? when i chew on menthol candy i feel alright?

sounds like you have 'Indigestion'. eat dinner several hours before going to bed and keep it light and not very spicy and keep your mouth closed while eating and eat slowly. As you do this and lose weight you should gradually feel better. If not you should see your MD

Reflux appears likely on described symptoms and would be consistent with rapid weight gain. Talk to your doc about your symptoms, losing weight will help in the long run.

If you are overweight, losing weight is imperative to address gastric reflux. You need to reduce your intake of food and increase your exercise. For healthy diet: http://www.choosemyplate.gov/., exercise 30 minutes/day, drink enough water daily so your urine is mostly colorless, have safe sex, no tobacco alcohol weed or street drugs. Get HPV, Flu and Covid vaccines. Wish you good health!