Hi Jana. If he were not eating enough, he would not be growing at all. As long as he is growing, he is eating enough.
He's actually getting a good bit of protein from the 12 ounces of cow's milk and the breastmilk. That's a LOT of milk. Breastmilk has the right kind of fat in it, so he's not suffering from lack of fats in his diet.
Pasta & cheese also provides protein. The pasta, the veggies and the fruits provide the carbohydrates he needs for energy. Can he eat peanut butter? PB on bread or crackers provides protein, fats and carbohydrates. Plus all these natural foods provide him with vitamins and minerals.
You do not want him to be fat. Just because there are percentiles for weight doesn't mean that he has to be in the upper percentiles for weight. You want him to be slender and healthy.
Remember that the more you stress out about his eating, the more resistant he will be to eating. Putting pressure on him to eat more than he wants to is going to drive him away from you, interfere in your relationship with him, and cause eternal power struggles between you.
Please relax and enjoy your healthy, active, beautiful child. ( :
Peace,
Syl