Hello
You wrote that you are 65kg now but didn't mentioned your height, because with your height and weight we can calculate your BMI..than you can get an idea that you are in ideal weight or less weight...
Anyway if you are still suffering from gastritis problem or any condition related to digestive system than you will face weight related problems..so go for proper investigations and use complete course of meditation...
Next Steps
coming to exercise just lifting weights will not gain weight here you need to understand that if you do physical activity for any muscle in your body it will get tone or definition but not weight..
if you want to gain weight so you need to balance your diet with workouts..
second thing diet is also plays an important role in
gaining weight so concentrate on calories which you are burning while doing workouts and amount of calories you are taking daily..
Health Tips
please consult a dietician before starting the diet and consult a gastroenterologists for your digestive problem..
and always do your exercises under certified trainer supervision...