CMoon, they say that women who are under- or low-weight tend to gain more during PG to compensate, if the body needs to it finds a way. It's hard to imagine now but you will find your hunger kicks in over the next few weeks and you might find you are naturally more hungry.

However, if I were you I'd be asking for a referral to a dietician, they will be able to help you with appropriate serving sizes, etc of foods that aren't going to aggravate the gall bladder situation whilst maintaining the level of nutrients that you need, especially in the later months of PG where most of the weight gain occurs. Good luck!