The general rule for rape shield laws is that evidence of prior sexual behavior by the alleged victim is inadmissible, but what you're wondering about would fall squarely into one of the exceptions: evidence of prior sexual acts by the alleged victim tending to show that injuries, semen, etc. came from someone other than the defendant are not prohibited by that rule.
I'm not at all familiar with North Carolina's evidence laws, but I'm almost definitely sure that they're modelled off of the federal rules because, well, that's what every other state does. I can't remember which rule in the FRE it is, specifically; it's somewhere in the late 400s, between 413 and 415.
Thank you. Another reason Sean Hannity should spend some time here is that occasionally he will learn something from an expert like yourself. Great post!!!