EBF Slow gaining 6 week old

Two weeks ago at our one month check up, my pedi told me that my son was only up 1 lb 1 oz. He was born 8.3 then was discharged from hospital at 7.10 then a week later back up to 8.1 and at our one month check he was 8.11. I bf hom no supplimenting and I began pumping the day the pedi told me he was "scrawny" her word not mine. At first I was able to only pump an oz maybe 2 from both sides, now I am pumping more. I give him a bottle of expressed milk once a day usually right before bed and he takes about 3-4 oz. I have a weight check for him tomorrow and I am nervous and feeling like I am failing my son. I highly doubt he is up another lb since last check.

My son is awake most of the day, alert, content, rarely fussy and nurses every 2-3 hours. Does anyone have similar experiences or advice? Thanks.