In both of my pregnancies I had "morning sickness" my first pregnancy was worse in this way than the second as it lasted well into the second trimester...I wasn't even able to keep down the prenatal vitamins.
My second pregnancy, however, was more like you describe in the way you feel. My problem was I was getting full very fast and then I felt nauseus (sp?) afterwards. I quickly found that there were certain foods I had to stay away from...any sort of mexican or southwestern dish would bring about vomiting in me...However, I could not eat enough egg rolls and constantly craved chinese food!.
My problem??? I was carrying twins...the extra body inside of me made it impossible to eat as much at a time so I had to eat smaller amounts more often, and with "morning sickness" I felt like I would not gain appropriately.
My doctor put me on a high protein diet. This not only increased my energy, it helped with the morning sickness, and it increased the birthweight of my twins so that when they were born at 33 weeks they were a surprising 4lbs 4.5 oz and 4lbs 9oz!!!! He had a wall of 10lb babies and twins that were 8lbs a piece...
I firmly believe that following this high protein diet allowed my twins to be healthy enough at birth to only spend two weeks in the NICU with minor issues versus the major ones that could have been a problem being born at 7 weeks.
So...having gone off on a tangent...I guess what I am telling you is...even if you are not carrying multiples causing the problems with your eating habits, your little one could have attachd in a place in your uterus when he/she sits in you stomach making it smaller and thus you eat less and still feel ill.
I would suggest eating smaller amounts. Try using ginger to help with any nausea...You can use the ginger in any form that will work for you, raw, cookies, pop, pickled, etc...but ginger is a natural anti-nausea herb. at only 8 weeks you are probably just feeling the effects of "morning sickness" on a "squashed" stomach.
You should check with your OBGYN and make sure you are not suffering any health issues...just to be safe...You might also ask if there is a possibility of your carrying multiples...I know in my twin pregnancy I gained weight at a faster pace and showed much earlier than with my older daughter...
Good Luck and congratulations on your pregnancy!!! ;-)