Burning pain & milk blister

Suzy
Ok so I have a burning in my left breast almost all the time. I also have what looks to be a milk blister on my nipple. Baby gets the most frustrated on that side and had a hard time nursing. I also have the most milk on that side. 
Any idea how to help or what the issue could be? Baby is 7 weeks. Not my first baby either! So I'm at a loss. It's not thrush either.