3 week old overeating ?

My bubs was born a chunker at 10lbs 5 oz. we struggled to nurse and he lost some weight and now at 3 weeks old he is 10lbs and 11oz.

I’m pumping between 3-5 oz. but my bubs is eating anywhere from 4-6 oz every 3 hours. In the evenings he wants more 😒 last night I fed him 4 oz of breast milk then after a hr of him crying and rooting around I gave him 2 oz of formula. Then 2 hrs later I pumped and he had 4 oz my milk again and he fell asleep for 4 hrs and when we woke up I gave him another 4 oz as a dream feed. This morning I gave 4 oz then again another 2 oz after him crying and he settled down.

Is it possible that my milk isn’t fatty enough and isn’t filling him up? I feel like I’m putting all this work into giving him breast milk and it’s not working. I pace his bottles too. Fed an oz. burp him a few minutes and continue. It’s takes about 8-10 minutes to get through a bottle this way.