Yanking on Nipple

G
My 9 week old has been yanking on my left breast during the second half of his feeding (we do one breast per feed). He doesn't de-latch and pulls quit hard. After about a week of this, my left nipple is feeling quite bruised.  He doesn't do this on my right breast. What could be happening? My doula said possible oral fixation development but I looked it up and am not so sure that's what it is...thoughts?