"even if I haven't eating more than a small snack in over 24 hours"
I just wanted to add... This statement above is not good. You're body needs more than this as it will begin to absorb muscle to nutrients. Some people who suffer from anxiety loose the desire to eat since anxiety affects the body globally. If this is happening you do need to push your self to eat.
If you're worried about weight ect... that's another story, but didn't see that above.
Is anyone pressuring you to eat when your not hungry which may cause food anxiety. You could also visit a nutritionist to evaluate your food intake. Anxiety will cause loss of hunger or increase in hunger and could affect your over all eating habits and levels of hunger.
My opinion with out more information is that this is an anxiety problem and I would also see a nutritionist to evaluate what you're eating. Size of meals can be offset by the value of the food and it is possible you are eating enough but I couldn't say. Chances are if you didn't have anxiety you may feel more hungry to want larger meals.
If you are concerned about your eating and your boyfriend is too, then there is probably reason for it. I think you are on the right track in talking to your therapist about your concerns. I don't think it matters as much to confirm if you have an eating disorder so much as to get to the bottom of what might be going on that is keeping you from being able to eat properly which, since you are naturally thin, could impace your health if you start losing weight.