Could be you need a different sized flange on that side? Also have you tried different fitting bras? If your boobs are different sizes then a looser/tighter fit could have an impact on the pump's position
I’m using a different size flange but hadn’t thought about bra fit, thanks @Hattie ! 🙌 x
Sounds like you've got a blocked duct. Keep an eye on it and make sure it doesn't turn into mastitis