Your question brought back so many memories for me. I hated drinking milk as a child, and I had daily battles with my parents all the way through elementary school. It was terrible.
I strongly recommend that you buy or borrow from the library a book by nutritionist Ellyn Satter called Child of Mine: Feeding with Love and Good Sense. The more you pressure him to drink milk (for instance, by cheering when he drinks or forcing him to stay at the table when he's not drinking it), the more he is likely to resist drinking it. He is entering a developmental stage where kids naturally get a little defiant as a way of establishing independence. You will be miserable if you make a power struggle out of his milk drinking, especially with a new baby on the way.
There are plenty of good sources of protein besides dairy foods. You can get children's supplements for calcium. My boys drink little to no milk, and they haven't had any growth or development problems.
I also agree with the other moms who've suggested that if he doesn't like milk, it may be because milk is hard on his digestive system.
If you can't tolerate the idea of him not eating dairy, just give him cheese, or make smoothies with yogurt and fruit if he likes those. If constipation is an issue, as it was for one of my kids, many pediatricians recommend a little Miralax mixed with water. Or, you could give him more fruit if he likes fruit.