My baby is 3 weeks old and I've just started pumping so we can introduce a bottle for when I have to go back to work (and so my boobs can have a break!). But the couple times I've tried I'm only able to get a tiny amount. The most I've gotten is 0.5 ounces (combined from both sides). I tried pumping immediately after feeding and I've tried waiting about 45 minutes after feeding. I don't think I have a supply issue because he's gaining weight and makes a ton of diapers. What am I doing wrong??