This has happened to a few of the women in my breastfeeding support group. They were advised to try different things like breastfeeding whilst walking around the home, bathing with your babe and dream feeding. Basically not placing any pressure on drinking from that breast
could be a flow preference, try feeding in different positions when on the right side like side or chest laying if flow is too fast (usually can cause gag) also pumping less preferred boob can even them out a bit
Happened to us too! Try different positions when baby is relaxed and not too hungry (football hold, side lying in bed etc) or express a bit before offering that side to baby.
Do you ever pump from that side to relieve it? My baby is only 3 months so I'm not as seasoned in the subject 🤣 My baby had a boob preference for a little bit and I was told to try different nursing positions on the side she didn't seem to want and it worked for us!