L.K.
just a second recommendation to look into sensory integration disorder.
Also--is it possible he had reflux as a baby and started associating food with pain?
Can you make smoothies for him?
Frozen fruit/veggies, protein mix (we have dairy/soy problems here, so we use hempseed shake mixes), some flax seed oil or other omega-containing oil, and milk?
You could add chocolate to that or vanilla...
(I love it with mixed berries and then a good scoop of cocoa *drool*)
There are a few fruit/veggie concentration mixes too--they might work well, but I haven't tried them.
I wouldn't force the issue at this point. Get some weight on him. keep him healthy.
He isn't doing this to make things difficult for you--I doubt he is feeling really good after not eating for 2 days :(
But hopefully if you get some weight on him, you can find what foods he will eat and slowly expand on the list?