I think it was a bleb. The photo on the Kellymom page really helped diagnose it. I stopped BF on that side for a couple of days, used heat and pumping to clear it. My LO had rubbed the tip of that nipple a bit raw when latching badly.
A few days later we had a breakthrough in our BF journey. He latched, squirmed a little and then the discomfort suddenly vanished. I looked down to check his latch and saw - for the first time ever - his tongue working away. He had also widened his latch. While Iowa watching he unlatched, opened wide with his tongue right out and relatched. Again, no pain. Amazing! He had just hit 5 weeks when this happened. I'd heard BF improved around this time but couldn't see it happening for us.
I partly credit the improvement to switching from the Medela Calma bottles to Breastflow. The Calma seemed to give him a lot of gas and didn't seem anatomically correct. I read about the Breastflow bottles on this forum and was thankfully able to buy them here in the UK. Watching him feed from them I could see straight away how much wider he had to open, and how much he had to use his tongue on the wider part of the teat to get the milk flowing. Much more like BF
So we now have about a 90% success rate for latching and I'm able to see EBF as a real possibility now. I just need to work on my supply