A few things. i am under weight, and trying to gain weight. its very hard as when i am hungry, i get full very fast. i take a high protien weight gain shake in the mornings...very high calories. i try to eat but its very taxing...i am skinny and well,

Problems: Two things: You might be reaching menopause - please see a gynecologist. Or you might have some emotional issues that are best handled by a psychologist.

Balanced diet?: First you need to rule out a medical condition causing you to have trouble gaining weight yet with frequent hunger. Your diet needs be more balanced with some fat and some carb as well since high protein diet is more conducive to weight loss than weight gain. On the other hand, if you feel well otherwise and are not anorexic , perhaps nothing needs be done. Try eating small portions when hungry.