Quoting Yurvette [♥]:" My son was a year and 18 lbs... Some just dont really gain weight. My son is 5 and a half and only 42 ... [snip!] ... a second opinion. The doctor sounds like a quack. If he is eating healthy and he is healthy, then there should be no concern. "
When kids don't gain weight on schedule, the doctors have to be concerned about neglect. Not saying that the OP is neglecting her kid, by any means, but the doctor doesn't live with her, so he doesn't know that. It makes sense that he'd be concerned.
My son's pedi sent us to see a nutritionist at 18 months. I took in a food diary to show that he was eating a lot of good, healthy food. They gave us some tips (Carnation Instant Breakfast in his milk, feed him ice cream at night, lol) and I kept him on whole milk for a while. He's 5 1/2 (almost) and he's almost 40 lbs.