It sounds like white spot? I had this and it was excruciating, and it was only on one side. No one, not even the HV or the doctor could help, a very lovely Scottish lady on the BF helpline diagnosed it. But it's very easy to cure! I suffered for two weeks before getting it sorted - how you have done 11 is a miracle!! The blister may be incidental.
Is the spot on the outside of the nipple? White spot is often not even a spot, just dried milk inside the nipple, which then sort of blocks up the duct as skin grows over it. Or does it just look like there's nothing there at all, but when you feed, it's like a hot knife being pushed into your nipple? I thought I had thrush as there was no other answer, but sounds like you know you don't as you have no other symptoms either.
Have a hot bath and get the nipple nice and soft and soaked. Then, with clean fingers, sort of try and look inside the top of your nipple, sort of gently pulling it open - you should be able to see some milky deposits - either a tiny spot, or just 'gunk'. Keep looking at the healthy nipple so you can see the difference. You should be able to gently scrape the spot/gunk with your nail, or, if you're feeling brave (and have gone beyond caring as i had), you can use a sterilized needle to just dig it out and gently push though. You'll know it's worked because you'll get the built up milk behind coming through.
It will still feel sore for a few days, but just keep doing the batch routine and it should go. I still check each time I have a bath as I seem prone to it!
Good luck! xx