It’s great that your goal is to have a healthy body! There is a big range of ‘normal’ body types in the world—some people are healthy at a skinnier weight, some at a heavier weight. It would be important to talk about this with your primary care provider who will have information about your height and weight as you’ve grown up, your parent’s body type, and would be able to consider if testing is needed to look for a medical reason for your low weight.
If you are very active and not eating balanced meals and snacks throughout the day, you are likely using more calories (energy from food) than you are taking in so your weight is lower than it should be for your height of 6 feet. Ask your primary care provider (PCP) about getting a referral to see a dietitian (a person who has studied nutrition and knows about healthy eating) who can help with suggesting nutritious and calorie dense foods. Other ways to help keep your body healthy include: seeing your PCP for regular check-ups and when you’re ill, exercising for 60 minutes every day, not smoking or quitting if you do, and avoiding alcohol and recreational drugs.
Read more about healthy eating: http://youngmenshealthsite.org/guides/healthy-eating/