It could be vasospasm, but I still wonder if it's a white spot (bleb). The pain you describe could be either, but the description of the white spot does sound like it could be the culprit. Also vasospasm would be more likely to be on both sides and worse in cold weather. Some mums find that they can clear a white spot by applying warmth for a few minutes, then rubbing it with a cloth - sort of like ex-foliating - to try and rub the top off it (gently!!). If you have no luck with that it might be worth seeing a different doctor (hopefully one who knows about breastfeeding!) and seeing if they can lift that skin off with a sterile needle. If you do manage to rub the top off, you should then be able to pull the built up milk out - like a string.

I really hope you find the answer and are able to feed pain free again soon. That is a long time to be in so much pain

BTW, I guess another option is to stick to one-sided feeding if that's more comfortable. Some mums do this for various reasons, especially with an older baby.