Breastfeeding on one side only

My son is 9 days old and since we left the hospital he hasn’t fed on my right breast. He cannot latch and when we were feeding in the hospital, I was in pain. Now that we’ve been home, I’ve been occasionally pumping the right side when it becomes engorged but even pumping on the lowest setting is hurting. Today I noticed though that my right breast is significantly smaller than the left (the side I breast feed on). Is this because my milk supply is lower than in the side he continually feeds from? If I start pumping my right breast after each time he feeds on the left side, how long do I pump for?

Thanks in advance.

P.S. have an appointment with a lactation consultant on Wednesday thanks to my doctor but it just seems so far away! And also my son is gaining weight normally and is always satisfied with just the left side.