Okay, so on a couple different occasions, my labia has swollen up to easily 3-4 times its normal size and also gets to be very tender after sex. This lasts for like a day. It usually happens after longer sex sessions in which I don't orgasm, and it doesn't happen with every person I have sex with. I'm pretty sure it's not an STD because I just got tested 2 weeks ago and everything was alright. I want to say this is normal, but I'm not entirely sure. Also, I noticed some light spotting during intercourse, but i don't know if there is any correlation between these two symptoms.
What can I do to prevent this, and is it normal?