Could my stomach became smaller because of vegetarianism and small portions of food? when i eat "too much" (bigger portion) i always have nausea

Bodies accomodate.: Our bodies become used to habitual patterns. If you have been eating small portions of food for a while, your system may go on overload when you eat a larger amount of food. It works the same way for other repeating behaviors. If you go to bed at a particular time, that is usually the time when you feel sleepy. If you eat meals on a schedule, your body sends out hunger cues at that time.