14 month old not gaining weight

Hey there everyone! It's been so long since I posted. Anyway, my son who is now 14 months hasn't been gaining much weight, in fact he loses some then gains it back. He weighs 18 1/2 pounds. His pediatrician has been doing monthly weight checks the last 2 months or so (he had one yesterday and lost an ounce) so she wants us to come back in 2 weeks. I'm not sure what she's going to say or propose. My son is still nursing but he also eats solids 3 times a day (about 1 and 1/2 jars of food each time). I know doctor's charts don't really mean a hill of beans, plus they're based on formula fed babies, but I just want to make sure everything is ok. What do you all think? My son looks good, you wouldn't say he's underweight by looking at him and he's very active. Thanks!

Nicole