I'm vegetarian and it is hard for me to get protein sometimes. I don't eat meat because I don't like the taste, so I can't get protein from it. I don't like nuts, except for peanut butter, so I don't get much protein there. I rarely eat any kind of beans, so that's another place I'm not getting a ton of protein from.
Really, one of the largest sources of my protein is tofu. I love it. And soy, if that has protein.
I had to take vitamins as a child because of the fact that I didn't get much protein or iron in my diet. Plus, they were good for me anyways. I don't take them now, but I probably should.
Have you tried meat substitutes? Like you said soy there but I'm asking just in case. Even though they're trying to emulate the meat's taste they're a bit more uh mild? usually and they're a pretty good source of protein :0 I absolutely loooove those Morningstar Farms chicken nuggets and corndogs oh my god (why can't they be available outside of the US ;_; ) but they have a load of different things you can try. Do they sell Quorn products in America? Since they make some good shit too ^^ And of course there's always eggs!!