how do i make my 19months old eat?

I tried not to feed him with foods that he ussually eat like sweets and junk foods, but he refuses to eat rice or even bread, i think he is closer to being underweight because he does not eat right, he chooses not to eat anything instead of eating what i offer him, he will just drink my milk, even though he's full breast fed baby i know it's not enough for him specially at his age, i know he has to eat more healthy, any advice?