not eating enough

ok a little information first

I am 5'6, 160 lbs, 28 yrs old
i have quite a bit of muscle on my body. my stomach is quite flat and small and i even have visable abs, but i also have some love handles. My hips and legs however are huge in comparison to my stomach. I look very lopsided with huge fatty hips and a tiny muscular stomach.

I do exercize regularly (p90x is the video i use most), but my problem is with eating.

I know for sure i am NOT over eating, in fact i am just the opposite. I do not have any kind of eating disorder, but i just cant eat enough.

my average day consists of
breakfast - a 'boost' breakfast drink
lunch - a piece of fruit and a cup of capichino
dinner - 1/2 cup pasta/rice, 2 cups vegtables, 3 oz meat
i dont snack on foods between meals and i drink at least 12 glasses of water a day.

My problem is that i just dont get hungry. And if i try to eat when i am not hungry i will get sick and throw up. I have been sucsessfull keeping down a breakfast drink in the mornings even thou i'm not hungry (75% of the time i can keep it in my stomach and throw up)

My concern is that i am just not getting enough nutrients. I have been eating this little all my life and just in the past 3 years have i gained fat (even though i am exercizing more and eating the same)

What can i do to be able to get more nutrients without the food coming back up?