Are you saying your child has eaten very little? Or are you saying that he hasn't eaten one single thing in 6 days??? If the latter, I'd make sure there's nothing else going on!
If he's healthy and just being obstinate, then I'd investigate whether he's sitting too long at the table. You say "I can leave the food in front of him for hours" and I hope you are being figurative in that way, and not saying that he has to sit there until he eats. I'd offer small quantities of quite a few foods - a few berries, a few pieces of chicken, a bit of pasta, some vegetables, etc. I even saw something the other day that looked intriguing: the parent used an ice cube tray to put small amounts of so many foods in front of their toddler. No junk, but a mix of tastes and textures.
Sometimes kids go through phases. Are you eating with him? A lot of kids really love to see what you're doing. I think it's okay to make a little activity of eating. You can feed each other, for example - that way, he's getting some food and some attention, but he's also using his own motor skills to manipulate a fork or spoon so he won't lose that ability. Meal time has to be fun, not just a requirement to sit still and eat. Of course you want decent manners (no food throwing or tantrums) but if he uses his hands now and then, it's not the worst thing in the world.
Trust your gut. If the doctor says to leave him there, but you've done that for 6 days and nothing is working, change it up.
You can also try taking him to the farm stands to pick out foods. Get excited about where food comes from, show him berries growing on bushes or carrots coming out of the ground, let him help you wash things (even if you have to do it again yourself!), and let him help in small ways to put things on the plates. Then sit down and "mmm-mmmm" your way through the meal. Take away the pressure.
You can also try some different settings. Sometimes an outdoor picnic or even a picnic on the family room floor can intrigue a child. Spread out a sheet, put some containers of foods and some special plates, and so on. Try dipping - a lot of kids will try a food if they can dip it in mild ranch dressing or hummus. Make a design out of food - you've seen the pancake house put 2 bananas for eyes and a strip of whipped cream for a smile, so try some of those tips with other foods. I've seen people make faces out of vegetables, for example - a curve of red pepper for a smile, carrot coins for eyes, shredded lettuce for hair, 2 pieces of orange for ears, 2 pieces of broccoli for earrings, some green pepper slivers for eyebrows, and so on. Make eggs in a special shaper or even a metal cookie cutter. Cut sandwiches into shapes even if it means you lose the crust. Why not?