Maybe try doing different kinds and brands of yogart. My friend once said something to me that made me forget about worrying if my son was getting anough nutrition since he wasn't getting any milk, she said that "Cows milk is for baby cows" and she was right, it's not the perfect combination for people, breastmillk is, so don't worry if he doesn't like it. And think about this, you never see any animal in the world, that nurses their young for 20 years, so if after a baby weans, it's not necessarily natural for them to drink milk for their lifetime.
My son is now 2 1/2, and couldn't be healthier, and to this day, never drank milk.