That looks like a strawberry Nevis birth mark; have the midwife double check it
My little sister, who is now 9 got this type of mark from her vitamin k jab when she was a baby and still has the mark to this day. Definitely nothing wrong or to worry about just the injection may have been rushed a little maybe as that’s why I think she ended up with one too? It looks sore but it didn’t irritate her. X
That looks like a birth mark would be likely unrelated to the vitamin k
I think that’s just a birth mark. Mine has a little one on her belly. Just mention it to the midwife and they’ll check it for you x