Any tips to gain weight?

I have been thin since I was young, and I had hoped that I would gain weight once I became an adult. Now, at 22 years old, my BMI is 17.2, which is considered underweight. My waist measures 25.5 inches, so it's a bit difficult to find bottoms that fit me. Despite being underweight, I don't look unhealthy because I do regular workouts and yoga. I have achieved the curves I wanted, but my weight remains the same at 43 kg. I eat a lot of rice since it's a staple in Asian meals for breakfast, lunch, and dinner. I also take vitamins, but I still don't gain weight. I have tried different diets, but nothing has worked. Is there anyone here who has experienced this or is experiencing this? Please help me if you know how to deal with this. Thank you!