What's Wrong?

For the past few months, I haven't been able to eat a whole lot. I'll feel hungry and I'll make something to eat, but when I go to eat it, I can only eat about half of it. I used to be able to eat all of it. I did have some trouble before with wanting to not eat to lose weight, but that was a year or so ago. I don't know why all the sudden I just can't eat as much anymore. I feel full almost immediately. Thanks!