i know y......

I do know that I do not eat enough calories to lose weight. It has been a problem for quite some time. sometimes I like to eat, but most of the time I just dont feel like eating. I have been this way for nearly 20yrs (since highschool). So my question is, how do I increase my calories to the appropriate amt? I have recently added green smoothies to try and help, since it seems easier to drink my calories than it does for me to eat them. Does anyone have any other tips or advise for people that simply have very little desire to eat? And when I do eat, I eat very healthy. I have no problems eating carrots and celery and half a cup of plain tuna for lunch and feel plenty full.