I’m beginning to write historical papers, but my background is in more narrative style writing since my major was in another field. In undergrad, it was DRILLED into us not to put our opinions or ideas into papers so I’m having the hardest time knowing how to analyze a primary source without feeling weird about it. Any thoughts?? Am I right that this is feels different because it IS different?
I'm not sure what plagiarism has to do with your question (inserting your own "opinions or ideas" is not plagiarism by any definition; plagiarism is when you insert other people's opinions and ideas as your own), but the key thing to keep in mind is that in a history paper you are making an argument. I don't think this is terribly different from other humanistic fields, except the type of argument is sometimes different. I don't know why you were drilled not to put "opinions or ideas into papers" — that's wrong in every field, and I wonder if you have misinterpreted what they wanted you to do. In a history paper, you frequently look at something that occurred (or some argument by another scholar) and weigh it against other things you know and think. This necessarily involves bringing in ideas and opinions. They must be grounded ideas and opinions; they cannot be just whims of yours, but have to have some relationship to historical evidence and argument.
If you were drilled to not do something like that as an undergrad, it's probably because they didn't trust you to do it well at that point. And it's unfortunate if that's the case — I try to teach my students how to form good ideas, good opinions, etc., and ground them, because that's the skill you need to learn in every field if you want to actually become an expert of some sort in it. I would ignore the "weird feeling."
If you need more elaboration on what I mean by "grounded," keep this idea in mind: imagine, in your head, is somewhat skeptical of your argument. What would you say or show them to win them over? What would they say in response? In a historical paper we are frequently trying to address an imagined critical person, because that way we end up formulating the strongest argument. If you think that your imagined critical person would at least be partially convinced, then you've probably done an OK job. In the real world, of course, there are non-imagined (i.e., real) critical people, and they are often more unpredictable than the imagined ones in our heads, of course!
In any event, it's hard to really get what you're asking about with a concrete example. If you gave us an example of the kind of source you are analyzing, and the kind of analysis that gives you the "weird feeling," it would be a lot easier to debug.