I just wanted to thank everyone so much for their replies. Although I wish no one else was in this same position, it helps to hear that I am not alone. Just to address a couple of questions/issues that people brought up.
My Dr has also suggested the high calorie diet. This doesn't mean a lot of junk, I just try to bulk up whatever he is eating to get more calories, i.e. more butter on his pasta. I also add Duocal, a calorie supplement, to his food & pediasure. He is also on periactin which is supposed to be an appetite stimulant. We've had mild success with it.
He doesn't eat a lot of junk, because he doesn't eat a lot, period. He doesn't really like most cookies, cakes, brownies, chips, or candy. He loves to help me bake & will have a couple of bites of batter but has no interest in the finished product. If we go to the grocery store & he can pick a treat, he usually picks either gum or sticky candy, like Starbursts. He likes chocolate but has no real desire for it. He just truly seems to have no appetite for anything.
He has had his glands checked and they were normal, but thanks for the suggestion. The esophagus thing is very interesting. I'm definitely going to call the school system for a reference, that is a great idea that I had never heard.
All of your suggestions about mealtimes were helpful. I feel like we've tried most of them over the past year & nothing has worked. I've tried feeding him on the go...I've tried having everyone sit down at the same time for a nice quiet meal...I've tried letting him watch TV during dinner...I've tried having him help me cook...everything seems to have the same outcome, very little food goes into him. Feeding him on he go as he runs around is sometimes just the least stressful as I feel like it takes away the control issues.
Someone asked if he eats better in certain situations. He does actually eat much better at restaurants. He eats a lot quicker and usually consumes more than at home. I don't know why this is but I do take him out to eat quite a bit just for that reason.
I know some people think its just a phase & hopefully it is but its hard to see him with his clothes off & he's looks like he's just skin & bones. I also feel like he has a tough time socially as other kids think he is a lot younger than he is. He often approaches kids at the playground & oftentimes they'll call him a baby...it's just heartbreaking. I purposely put him in a mixed age preschool this year just so he wouldn't be the smallest one in the class. He also doesn't seem to have a ton of energy which concerns me as well.
Over the past couple days, I've started to cut back on his Pediasure to try to see if that's filling him up. So far, it doesn't seem to be making a difference, he's still not eating much but I'm going to try it for at least a week to see if it makes a difference.
Again, thank you to everyone for your advice and support, I REALLY appreciate it. If anyone else has any suggestions, I'd love to hear them.