Honestly, what matters most in my opinion is that your recommenders know you VERY WELL and are ENTHUSIASTIC about writing one for you. You don’t want your LOR to regurgitate your extracurriculars and your stats.
I know a lot of people say it’s best to get at least on rec from humanities and one from STEM, but again, the LOR is supposed to paint a picture of you not otherwise conveyed in the application. So if that means your LORs come from all english or history teachers, that’s ok. I guess it’ll also help show other sides of you and how qualified you are in other areas as well.
I’m also a current high school senior applying as a STEM major, and while I have pretty good relationships with all of my teachers, I asked the ones I loved and knew the best. That meant asking my sophomore year Honors Math an Honors English teachers and my current AP Lit teacher. (They also say it’s best to ask junior or senior year teachers, but with the pandemic, I didn’t really get to know my jr yr teachers last year as well. But to reiterate, pick the people who know you) The key detail is that they said they “would LOVE to write me an LOR” and “with most students, I say yes to be nice, but I don’t really know them that well. For you, it will be easy.” You don’t really want to be one of those kids they are just trying to do a favor.
So in your case, maybe hold off on the third recommender. Their letter might end up sounding bland and the admissions officers probably will see right through their letter.