Why is my 6 week old breastfeeding like this?

I’ve been breastfeeding my baby and bottle feeding (pumped milk) as needed since he was born, and we have been almost exclusively breastfeeding for the last few days. About a week ago he was taking 3-4 ounces in a bottle with a break midway through. That only lasted a couple days before he went back to 1.5-2 ounce feeds.

He only breastfeeds for 5-10 minute sessions and tends to feed more frequently, about every 1.5-2 hours. He’s 6 weeks old and gaining weight well, has s good latch, and falls asleep while feeding often. I also have a heavy letdown and make quite a bit of milk. I’m just concerned that 2 ounces is such a small amount for a 6 week old.

Is this sort of feeding pattern normal? Am I doing something wrong for him to not be eating 3-4 ounces every feed or feeding more than 10 minutes at a time?