I don't eat enough - how can I introduce more food into my system?

[Jitter]

A normal day's eating would consist of ice (yes, I am aware this is weird) and a small handful of grapes (five, maybe six) for breakfast, lunch is half a peeled apple and a few pumpkin seeds, dinner is whatever is cooked, normally healthy homemade dinner - about 500kcals.
It's not that I'm underweight or anything, I don't know why I don't eat enough, I just don't feel worth it and I feel really bad when I've got it in my system, hence I tend to exercise as much as I can whenever I've eaten something, such as dinner. Whenever I'm out with friends and they eat, I just feel like an idiot and everyone always asks me why I don't eat, it gets really really annoying.
I know I need to get over this, so I was wondering how I could introduce more food into my system? If I just increased it all suddenly, I think I'm more likely to vomit it, not by purpose or anything.

I'm 17. I don't really want to put my weight/height here, sorry.

 

[MatthewM]

You'll be fine as long as you eat enough fruits and vegetables. I wouldnt worry about how many MEALs I have though.