Hickey like rash

So basically I had an itch on my boob and naturally I scratched it cause it was a bad itch! But after I did it I looked to see if anything was in my bra that could’ve made it itch (wearing a sports one cause it’s lockdown and they’re comfy!) And I noticed it was marked, and it looks like a hickey!

I’ve never had this happen before, anyone know why it could’ve caused it and if it’s anything to worry about? I itched my thigh and stomach (quite hard) to see if similar marks came up but it didn’t! It doesn’t hurt at all and no itching since, just looks like I’ve given myself a hickey!!

I’ve uploaded a photo to see!