I understand why you removed the post, but I had a similar experience, but thankfully it was concluded much quicker.
Look in your red book, is there any mention of the mark at birth?
Go through all your photos, are there photos with it in by accident (rather than deliberately taking the picture) collect all that you can to show timeline.
Take photos every day from now on, it won't fade if it isn't a bruise, makes notes, mine child's got worse in hot or cold, and when they were unwell.
This won't last much longer as the professionals will realise that it isn't fading.