Broken blood vessels?? Help

Sooo I was having sex we got a little into it and my boyfriend was smacking my ass fairly hard. I didn’t think much of it. Today I was in my bed and my sister was like ummm wtf is on the side of your leg cause it looked like a rash. It’s like small purple dots in a pretty large cluster they’re kind of spread apart. Has this ever happened to anyone? Is it dangerous? I’m not sure if it’s exactly from that cause it’s kind of on my leg instead of my butt but I don’t doubt he could have smacked me there.. help