Can't figure out why my 13 month old is not growing, any suggestions?

My, now 13 month old, has been having issues with growth starting at about 9 months old. He was born 8lbs 12ounces, and 21 inches long. He was at the 50th percentile for his weight and the 85th-90th percentile for his height up until around 9 months. When we went in for his 9 month checkup we found ou that he had dropped to the 50th percentile for his height and the 5th percentile for his weight. He had only gained 4ounces since his last checkup. They referred us to a nutritionis who gave us a list of reccommended food and spreadables and addables. He was placed on a high calorie diet. We have strictly stuck to it, trying to give him no less than 1700 calories a day. He gets between 3-4 boost/ensure drinks a day, along with all the high calorie food we can pack in. He gets all the bad good stuff the nutritionist reccommended, like the pancakes and waffles for breakfast, as well as still healthy stuff like eggs and bananas in addidtion to.

[concernedmom18115]

We went in for his 12 month checkup and he was below the 5th for his weight and back up to the 75th for his height. They performed blood tests, fecal anaylsis, urinalysis, and a sweat test. We have ruled out Celiac disease, cystic fibrosis, and parasites as well as determined that he has no thyroid issues. We took him to the hospital about a week and a half ago because he started refusing to eat and he threw up. They performed more blood tests, which came back fine, and did a chest and abdominal x-ray, which showed no problems either. They asked if we wanted to hospitalize him, but they couldn't give him any treatment, it would just be monitoring. We told them that we had an appointment with the Gastroenterologist at the hospital on the 7th. They told us that we needed to keep the appointment, obviously, and that they couldn't really do much more for him until the GI has a look at him. We opted out of the monitoring as they though it wasn't the best option and we didn't think so either. We are monitoring him at home and they would have been doing the same things, given the absence of the GI's statement. We had a WIC appointment last Thursday and he is now below the 1st percentile for his weight and his height is at the 27th percentile... He lost 2ounces.We're terrified. I know the GI appointment is coming up, but he seems to wasting away and is getting tired all the time now and refusing to eat more and more. He threw up again today, everything he ate. He had only had two boosts and half a banana. When he drank some water, he vomited everywhere, everything. i'm just wondering if anyone has any ideas, because we are so scared right now. Please help if you can.
A worried mommy
(Jamie)