Laura,
Gastroparesis is one of the first culprits they check for when there's not another likely culprit. Have you had a gastric emptying study? (This would have involved eating scrambled eggs with a radioactive tracer in them, usually along with a piece of toast w/jelly and a glass of water, then a series of scans at different time intervals to see the timing of the food emptying from your stomach. The entire test typically takes several hours and would usually done through the radiology or nuclear medicine department at the hospital and frequently would be ordered by a GI specialist, though it might be your dysauto doc that refers you.)
Gastroparesis can cause nausea and loss of appetite. You might want to google around about that and see if that seems to fit the bill, and/or talk to your doc about it. We have several folks here who have it and are being treated for and many more who have at least been tested for it at least once.
As for increasing calories and nutrition when you don't have an appetite (and I'm really feeling guilty giving you advice on this right now, because I'm currently having the same problem and I'm doing a terrible job of this myself ... so in all fairness I admit that this is "do as I say, not as I do" advice):
The key is caloric density. Most likely the volume of food is what triggers you the worst, so the more calorie- and nutrient-dense foods you can get, the better. (I.e., higher calories and nutrients in lower volume/area so you don't feel so full.) Nuts are high in heart-healthy fats (and ooh, you can get SALTY ones ... it's SO hard to get salt in when you're hardly eating, isn't it???) and are thus calorie-dense. The serving size is quite small for most any type of nuts, so those are a good choice. Someone else mentioned cheeses, though the issue there is that cheeses are a great source of nutrients (esp the stuff we women need for bone health!!) and both protein and fat for calories, but unfortunately it's not the heart-healthy kind of fat ... so you've got to mind that trade-off, particularly if you have issues with high cholesterol and/or heart disease yourself or in your family history. Of course there are reduced-fat varieties, but then you're not getting the same caloric benefit anymore.
I haven't tried it (except eating storebought cereals that happen to contain it), but flax seed has been recommended to me; the nutrition info checks out!
http://nutritiondata.self.com/facts/nut-and-seed-products/3163/2
With 150 calories/oz, and the ability to "hide" ground flaxseed in other foods (or at least that's what I've been told), it might be a good way to help boost your daily caloric intake. According to NutritionData, it's a "good source" of 3 nutrients, and a "very good source" of 3 other things including dietary fiber (mmmm, fiber!) plus it has those omega-3 and omega-6 fatty acids ... so it's not just empty calories or "bad" fats.
NutritionData also has categorizes foods that are "better choices for weight gain," so you might want to browse through the various sub-categories there:
http://nutritiondata.self.com/foods-000996000000000000000.html
If you're looking for a way to track how many calories you are taking in each day, you might want to try MedHelp's food tracker if you're not using that already:
http://www.medhelp.org/user_trackers/gallery/food?
(There are also trackers for weight and water intake that you can link to from that page if you want to track those as well.)
I hope I've given you at least some info that may help. I am seeing my doctor this coming week and plan on bringing printouts of tracking I've been doing of my calorie intake to share with her to help discuss the problem. I've been tested for gastroparesis in the past, but am not sure if a retest might be in order in case things have changed in this regard. I'd been suspecting that my loss of appetite was related to the pain I've been in of late, but it's just so hard to say. There are times when the pain isn't *SO* bad, and it still feels like eating is a chore, that food is entirely unappetizing, and that if I eat more than what used to be "snack size" amounts to me I feel ill.
Take care of yourself, and keep us updated!!!
Heiferly.