Did you ever try soya? Nuts have a lot of protein too (though healthy fat too, don't eat too much). Also you can eat quark (curd), cheese, fish, chicken....
Protein is good. Of course, if you eat more calories than you burn, you will gain weight - no matter where the calories (energy) do come from.
How about casein protein? That's the other dairy by product. It's good for slow absorption, they say. Cottage cheese is a good source. They also make shake mixes with it. I use a raw vegan protein called Sun Warrior to supplement my whey protein. It's kind of expensive. There is also hemp protein, rice protein... There are a whole lot of commercial products that are not whey based.
Depending on your exercise program, you can likely get most of your protein from food sources. Tuna, chicken, brown rice & beans, salmon, nuts are more a good fat source with a protein bonus, eggs are a great source...
Protein is supposed to be good for gaining muscle, but of course you gotta push hard in the gym to make your body need that protein.