Hi Flowerpot
We've chatted on another thread but thought it worth answering your question here, to help anyone who might search the forum in future.
Blood blisters can be one of the symptoms of a condition called Lichen Sclerosis which often presents with intense itching and burning, amongst other symptoms, so can be misdiagnosed as thrush or vaginal atrophy.
There is a brilliant FB group called Lichen Sclerosis UK Support Group that is worth joining to read about it and get links to reputable and trustworthy sources for further reading.
And, of course, get yourself checked by GP to be sure there's nothing else that needs investigating.
Susie