What is this mark on my 3 week old?!

What is this??? 😩😩 we found it on Tuesday when we were giving him his first proper bath... it was like this....

We took him to the doctor that day and she said that it’s likely a birth mark but that she wanted to see it again on Friday.... so we took him again.

She ruled out it being a bruise (we knew it wasn’t) but she said that they want to keep an eye on it, so we have to take him to the hospital for an appointment. I looked at it today and it seems more visible...

Has anybody seen this before?!? Anything similar?? The doctor knows it’s not a bruise, thinks it might be a birthmark but doesn’t seem confident......

I’m so scared, he’s so precious to me 😔 x

UPDATE!!

It’s a birthmark! Confirmed today!! The doctor just wasn’t sure due to him being a duel heritage baby but all confirmed he’s very healthy and happy!! ☺️☺️💕💕