Yes, Low supply can have block ducts too! Get a hot compress and roll it over your breast, massage on the block area and pump it immediately. It takes a few tries for it to be fully unblocked. For milk blister, use a sterlized needle and poke it.
Back then when this happened. I always took a warm shower. And whilst in the shower message my bresat gently. it for better after a few days. However I don't pump, only exclusive breastfeed.
Try massaging your breast and stimulate the flow. Do you latch? Latching helps.
mei