That part of your leg bruises like crazy!! I had a dog bite me just above my knee on the back of my thigh, and when I say bite, like the dog was being playful and excitable and it’s teeth literally just caught my skin for a second...didn’t hurt at all at the time and even the rest of that day, the skin was a little pink and I had a couple of teeth marks but then as the days went on...omgggg my bruise was just like yours Lid, was getting bigger and bigger and darker and darker. Took weeks to heal and eventually faded to a yellowy green and thankfully no scarring. I think it’s because we have so many veins close to the surface of the skin on our thighs so it’s a sensitive area.