My intolerance to cow's dairy started as a child (about 10 years old). My father used to force me to drink my milk for breakfast, but I always whined and complained that it make me feel terrible and hurt my stomach. But, he wanted my bones to grow strong and figured milk was the answer.
When I was old enough to choose my own morning beverage, it definitely wasn't cow's milk. Basically, I haven't drank cow's milk since I became a teen and I'm MUCH happier and less bloated.
I did, however, still enjoy cottage cheese and yogurt. One of my favorite high-protein combinations was cottage cheese with vanilla whey protein powder and slivered almonds. Another I enjoyed was plain yogurt with ground flax seeds and vanilla whey protein powder. But... as of about 6 years ago, my body just stopped being tolerant to all dairy, no matter what form it was in. And, the issue wasn't just lactose, because I tried all the Lactaid and low-lactaid products you could imagine (i.e. mozzarella) and it did no good. I really suspect the issue is the casein milk protein because if I eat anything with that in it, I get a ragging headache and intense bloating. Not fun. Whey protein is only a problem if it's not highly purified and contains added digestive enzymes. The brand I use and recommend to my cow's milk sensitive clients is Dymatize Elite Whey Protein Isolate. It tastes great and doesn't come with the gas and bloat that other brands of whey can sometimes cause.
Some people feel that adult on-set allergies are not really due to our body becoming intolerant to a food, but to the fact that our food supply is completely overprocessed and contains more preservatives than it can handle. I tend to agree. For example, my issues with dairy became worse when I moved to the US, versus only somewhat terrible when I lived in Canada (who has different milk processing methods).
In any matter, I don't have to worry about cow's milk any more (or miss yogurt). I've now discovered the wonder of goat milk . Through this wonderful little animal, I can now enjoy goat cheese on my salads and omletes, and goat yogurt for a mid-day snack (with nuts and nutritional yeast :) ).
If your body really has an issue with cow's milk, I encourage you to give Goat's Milk products a try. They really taste good and give you the chance to love dairy again without the discomfort.