Not producing enough?

Visited the pediatrician yesterday for our 3 month baby wellness check up & for the last two visits they said my son has been dropping off the growth curve for weight. He was born 7lbs 7oz & at his 2 month check up was 11lbs 11oz & at this recent one he was 13lbs 4oz. The pediatrician said he probably isn’t getting enough calories from me Bc he thinks I’m not producing enough milk. However, my little man is bottle fed 3/7 days a week & gets 3-4 oz of expressed milk in each bottle and eats every 2-3 hours, plus when I pump I will get 3-4 oz average from each breast in a session? I thought I was producing enough or do I need to increase my supply?