"It was so much harder than it had been with my two older kids. Nothing would make Charlie happy. I just felt, this is really, really difficult," says Mary Jo who lives in the Chicago area with husband Chris. "After a series of long days and nights of crying, I finally called the pediatrician. He said, 'I've never told a mom this before, but I think you should stop breastfeeding.'"

So she did. She switched Charlie to the formula the doctor instructed, which helped the colic. His temperament improved and he seemed a bit happier. But as the days slipped into weeks, Mary Jo noticed that Charlie wasn't gaining weight and didn't seem to be growing the way her other babies did. She mentioned it to the doctor at a routine baby check up.

At 8 months and well below average on the growth chart, Charlie underwent an absorption test to check it out. After a false start, results came back normal. The gastroenterologist told her to add extra fat to the little boy's diet. By now, Charlie was eating some table food, including bread and pretzels. Mary Jo mixed a tablespoon of melted butter into his food at each meal. After a month or so, his weight began to creep up. The doctor pronounced the baby cured, advising Mary Jo to continue adding fat to his diet.

As the months passed, Charlie's energy flagged and his disposition worsened. He cried whenever Mary Jo left him with a babysitter and didn't calm down until she returned. He developed constipation. He was lethargic, cranky and clingy, insisting that Mary Jo hold him.

"He couldn't stand for me to put him down. He wanted to be in my arms all the time or sit in my lap and watch Barney videos," she recalls. "A toddler normally has boundless energy, but I remember taking him to an indoor playground, a toddler paradise, and he didn't even want to get out of the stroller."

One day, Mary Jo was grocery shopping, standing at the bread counter with Charlie in the cart. Unexpectedly, he threw up.

"He hadn't been sick," says Mary Jo. "Usually you can tell when something like that is coming, but there was no warning."

A week later, Charlie vomited again – and then again, for the next five weeks. Mary Jo took him to the pediatrician who ran a series of tests. Charlie hadn't gained any weight since July – and this was October. Mary Jo was increasingly concerned, but with the tests coming back normal, the doctor was reassuring.

"He said that sometimes kids plateau. And not to worry about the vomiting, as long as he was a good eater, which he was," she says.

As the weeks went by, Charlie would have wailing episodes, sometimes lasting an hour or so, as if his stomach ached. At one point, he was in such distress that his parents rushed him to the emergency room. The crying stopped by the time the boy saw a doctor, who said it was probably "gas."

At Thanksgiving, as Charlie, now almost 2, was fussing and clinging to Mary Jo, the worried parents shared their concerns with Chris' cousin, a psychiatrist.

"We told her, 'We don't know what else to do; the doctors keep saying that he's fine,'" says Mary Jo. "She told us, 'Charlie is not fine. He needs to see a neurologist and a gastroenterologist – right away!'"