If it makes you feel any better, my son at 15 months has become a picky eater even though he has always been a great eater. Mealtimes are a battle, he wants to get down and play or climb onto my lap, or climb on the table I think at this age it has a lot to do with making choices and asserting likes and dislikes.
I try to make sure that the things he does eat are nutritious. After nap every day we make a smoothie with whole milk yogurt, fresh fruit, frozen berries, juice, flax seed or Udo's oil, and powdered greens mix (cause getting greens in this child is impossible). Do you think your son would like a smoothie? It is SO tasty. You can load it with other things like avocado, bran, wheatgerm,etc.