I would trust my body and my appetite more than any daily caloric requirement estimation. Those things are not universal. They can be way off for some people depending on your body composition, the types of food you are eating, and all sorts of other things. At one point a few years back when i was doing calorie counting, i had to drastically undercut the recommendations to get my weight to come off, and I was actually measuring my food for accuracy with a food scale. Then when I switched to a low-carb diet, I ate more than the recommendations, and lost faster.
And also, you won't waste away. If you aren't hungry then you don't need food unless there is something seriously wrong with you (which is possible, I suppose, but not likely). If you start working out, your appetite should increase naturally.
It is possible that you are skinnier than you want to be, for cosmetic reasons or whatever, but if you aren't having any symptoms of malnutrition, it is very unlikely that you are unhealthy unless you have some kind of wasting sickness. Cancer, for example, can cause you to lose down to the point of emaciation even though you are eating enough, so if you really are wasting away while eating till you're full, you should see a doctor and make sure it is nothing serious.
If the situation is not quite that serious, and you just want to do something that will increase your appetite to gain a little more weight, bring in a few more potatoes, rice, and that sort of thing. A lot of paleo people who don't have weight problems are incorporating rice and potatoes and sweet potatoes with good results. Many agree there is nothing actually unnatural or non-paleo about potatoes and rice, but they can be a problem for people who have developed problems with insulin resistance.
Also try eating more fruit.
