Blood blister on vagina?

Anyone know what would cause this? We noticed it 2 weeks ago and it was a small black bump which we assumed was a little blood blister. It appears a little bigger in size now and the red on the outside is new. Any reason this should be seen in office?

Hello!  I'm afraid that this picture is a little bit blurred on my phone, but one possibility for this is a tick (smooth body, apparently immobile, attached only at one end).  Another might be a haematoma which could imply injury or a blood clotting problem; another could be a tumour, benign or otherwise.   Insect or other bites and  trauma are also possible.  Given that the lesion is growing and bleeding, I would say that a this merits triage (eg calling the vet or emergency vet to see how urgently they'd like to see you) which is likely to lead to an early veterinary appointment.