Does anyone know what this is?

Update !!!!!!

I just went to sleep to see what it does & it’s gone. I wasn’t by any heat so i really don’t know what it was. It’s never happened before so if it Happens again I’ll for sure go to ER

UPDATE #2 :

I’m so sorry I haven’t been able to update. I went to the doctor and they weren’t very concerned which I was confused about. They said it would probably be from heat and I explained that I wasn’t around any heat at all. And after that they said that it could be from my circulation not flowing good or something??? But here’s the weird thing. A few days after I went to a bonfire and it happened AGAIN but on my thighs? So then I figured it would be from the heat. But I wasn’t around any heat at all the first time and nothing was on my lap?