I'm underweight sir give some tips to gain weight?

Further tests needed: First you will need to be evaluated to rule out causes of underweight which include hyperthyroidism, adrenal insufficiency, celiac disease, stress/depression and certain medications. You should see an endocrinologist for the proper tests. Hope this helps!

Get evaluated: First, how do you feel? The "ideal weight" charts are subscience and should not be applied to individuals. Most Olympic track-and-field athletes are "underweight" and solid-muscle football linebackers are "obese". A woman needs only a little body fat, and enough muscle to enjoy recreational activities. If you cannot maintain this, you may have malabsorption, thyroid disease, or some other problem.