Eating disorder?

What would you consider this?

I have trouble eating my whole plate of food. I can literately eat one slice of pizza or 2 chicken nuggets from a 10pk and call it a day. I’m never really hungry but when I actually eat more than a slice off my plate I feel as if I overate and it’s been making me really sick to my stomach. Any thoughts on why ? Or has someone went through a similar situation as I? Also if it makes a difference. I weight 138. My weight changes a lot but never passes 140. And never goes below 130. Not doing it on purpose. Im fine with my weight.