Why am i always ill, and thin?

Eat more protein, less sugars and fats. Exercise more outside... but wear sunblock and shades. You need more of an active, stress free life style. You're adrenal glands may be producing too much cortisol... because of stress. The fact the you're 15 may be the biggest reason for your dilemma... you're still growing into your adult body shape. Don't stress, you'll be fine. You may want to try Cranial Sacral Therapy, for your congestion and headaches... also it will relieve stress.