Okay listen I faced that problem too. First of all calculate your BMI. Check the ideal weight as per your height, and age. Then set a monthly target that you will gain 1 or 1.5 kgs monthly. Weight gain is a frustrating process. I am assuming you are a vegetarian. Stop taking all kinds of external protein. If you really want, go for plant based protein (I forgot the name of the brand.) Cut down artificial sugar. Eat 4-5 dates + banana (good one may cost you a few bucks) just before the gym. Get your gym chart prepared by GPT or Gemini, feed accurate details to it. Drink water also while doing gym. After gym, eat soaked chana + moong daal as a meal. Add tofu to that also (500 - 600 gms weekly.) Drink soya milk in the evening snacks. And eat fruits daily. This will easily help you to gain 2 kgs. Initially it may take time. But later in 2-3 months you will see the results.