J.G.
I have had the blisters before & also clogged ducts... they can take a few weeks to heal sometimes. I know with the clogged ducts I was told to put the baby's chin lined up with the clogged duct. So if the clogged duct is on the lower side (under) I had to lay on my side & nurse laying down tummy to tummy... I hated that possition, but it did help. Since where ever they chin is, they have more power or sucktion. Also, sometime the blisters are caused by improper latch... make sure you get as much of the nipple & brown area around it in the baby's mouth as you can. If you need to extract a little milk to get that area a little softer so the baby can latch better.
Oh, sound odd... but milk will help heal your nipple. Make sure that you let a little milk out and on the soar/blister. Then air dry - it will help to heal the blister.
I wish you a speedy heal... keep trying - I know they hurt! But you are doing the best for both you and your baby. If it dosen't heal soon - go see the doctor.