6 month old has a growing birth mark, do I get it checked out?

[Mummypig2016]

My husband says I'm over reacting so I thought I'd ask you guys 😂
It was very small when she was born but had doubled in size. She keeps scratching at it too. I googled birth marks and it looks like the common salmon patch one but when she cries it turns purple. Would you go to docs? Feel a bit silly, like I'd be wasting their time

Of course I'd get a rash checked that has doubled in size and is obviously irritating her!!! Can't you ask the HV or MW instead of GP?