Hey there, Sodabutt (great handle!).
So, one thing to know is that it's pretty common for menstrual cycles -- how they feel, when they happen, what they look like, how long they last -- to shift quite a few times in life, not just once.
That said, I am a little bit concerned about that unusual cramp you mentioned, and with the issues you have walking and thigh pain. Do you have access to healthcare so you can talk to a provider about this (even if it's telehealth for now)?
In terms of asking if something is arousal, I think it's important to see arousal as more than just physical. I think making it only physical robs us all of some agency, and, of course, our bodies acting in a way can't speak for our feelings, you know?
That area you're talking about is the vulva. Here's some basic info about it here -- Innies & Outies: The Vagina, Clitoris, Uterus and More
-- and a little more that might be pertinent to questions about those body parts and sexual sensation -- With Pleasure: A View of Whole Sexual Anatomy for Every Body
What you're feeling might just be circulation, honestly, and just...well, having a vulva. When you ask if it's arousal, do you feel like you're having sexual thoughts or feelings when that's happening? Sexuality isn't just other-directed or influenced, so we can have those feelings and either not have them be about sex with other people, or have them and still not want to have sex with other people.