Birth mark or something else?

My baby girl just turned 2 months old on the 10th. I was getting her ready for bed tonight when I noticed this mark on her ankle. I can’t imagine that she’s had it and I just never saw it but it seems so odd that it just came out of no where. She literally just had her 2 month check up yesterday and I didn’t notice it then and neither did the doctor (at least she didn’t say anything) but she did get her shots yesterday. I know this might seem silly to even question but does it look just like a birthmark that all the sudden came out or is it something else I should I be concerned about? I always thought that you had to have birthmarks at birth 😂 I never knew you could get them later on into I started trying to look into it.