Question

Do NOT do Testosterone boosters. You are too young (by about 8 years) and it will likely cause problems for you down the road. That said, get your blood work done. Maybe your thyroid is too active or there is some other hormone imbalance. You can't know unless you get your blood lab tested.

You also want to make sure you are digesting your food properly. Probiotics and enzymes would be a good start to help your body get all the nutrients it needs.

Beyond that weight gain is typically done through over consumption of calories. If you are not a big eater, then you may have to drink your calories. Growing up I regularly drank 2-3 dozen eggs a day. Vince Gironda taught me this method. Start with 6-12 eggs and slowly work your way up, adding 2-4 eggs at a time until you reach your limit (you'll know your limit.) Yes, these are whole, raw eggs (preferably free range... it does make a difference.) Mix them with either heavy whipping cream, or half and half. And you can use a protein powder to flavor (good whey protein often works well... I prefer MTS brand.) Only use a blender if it can stir very slowly. Do NOT use a high speed blender. OR you can simply shake them up in shaker bottles. Drink this shake though out the day in between meals.

Good luck, enjoying eating, and get cracking :)