Why can't youeat more than one meal a Day

Maybe what you eat for lunch contains large amouts of fibre, and as you know fibre 'grows' in your stomach, therefore fills you up for longer (for me its very long). If you think this is affecting your concentration in school etc, you should cut down on fibre and switch to other foods. Try get down the gym too, as it should increase your appetite ( but you will only gain healthy muscle if you keep exercising )

some tips on how to get bigger biceps and triceps

if you want bigger biceps andtriceps you need to do specific exercises to target these areas, such as bicep barbell or dumbell curls, tricep dips, close grip bench press, tricep extensions. also you need to eat the right food to build that muscle and that food is protein and carbs, but to build muscle you need to eat 1g of protein per pound of bodyweight so for example if you weigh 150 pounds then you need to consume 150g of protein a day.

here's a website to show you some bicep/tricep video exercises

http://www.thefitmap.co.uk/exercise/tool...