Hi welcome -i can advice to add one protein supplement like proteinx or kabipro / b-protien 2 scoops two times with 150 ml milk. Or lukewarm water.
Diet- you need high calorie diet. That means you have to add quality meals enriched by protein. Add more rice in meals added by butter or ghee, some times fried rice or polao you can. Vegetables soup or strew 2 times, maximim mix vegetables in meals, 2- pcs sweets. In a day. Add sprouts, pulses. Add puddings cream paneer, yogurts, curd as possible. 2 pca big size banana like in break fast & at 11 am. Sleep min 8-9 hours. No stress, more water, electrolytes, fruits juices, banana shake, more importantly add enough protein by milk (d. T or skim), chana, curd, lassi, butter milk also better. Finally I can advice to add one protein supplement.
You should go for specific Diet by a dietitian. Once you follwo for two- three moths then surely will get fruitful results.
Tips which can help you in gaining weight -
1)Eat small and frequent meals , if you are eating 3 meals in a day break them down to 6 and try and have meals every 3-4 hours.
2)Even though you might feel that eating a burger,pizza with some coke and mountain dew would help you in gaining weight ,Beware!!.These foods can make you fat in the long run.Eat good and healthy food by that I mean good amounts of protein,healthy carbs and good fats.You need to build muscle and not a storehouse of fats.
3)Eating protein rich foods i.e foods like milk,paneer,chicken,eggs,fish and cheese becomes important because without enough protein in the diet the entire food would end up turning into carbs and ultimately fats.
4)Eat calorie dense foods like nuts(almond,walnut,cashew,pecan nuts,peanuts) and good amounts of fruits and veggies.
5)If you have to eat carbs then make sure you choose complex carbs like oatmeal,brown rice,quinoa and barley.Do not have too much of simple carbs(candies,doughnuts,pastries,cakes),remember these shall make you plum and not healthy.
6)Exercise!!Yes weight training can be your best friend if you have to put on weight and build some muscles.Resort to compound exercises like squats,bench presses,chin ups,pull ups and dips.
7)Sleep well,by that I mean sleep for at least 8 hours and while you are sleeping the body is building up some muscles.
8)Do not skip meals as if you have to gain weight you need to eat frequently.
Last but not the least remember with muscles you would gain some fat ,but thats completely ok.Eat less of refined ,processed and high fattening foods and you would be left with a killer Physique.
In case you need to know anything please feel free to get in touch with me :)