Re: Do I have a supply issue?
Welcome, and congratulations on the new babies! It sounds like you are doing an absolutely fabulous job.
The pattern you describe, of near-constant afternoon/evening feedings, is 100% normal, particularly for such young babies. Most moms have a bit of a supply dip in the later hours of the day and this, combined with a baby's normal tendency to get tired and cranky as the day wears on, causes babies to "cluster feed" at the end of the day. The best way to get through it is to roll with it. Just nurse on demand, nurse as much as possible, and the babies will eventually train your body's internal clock to make more milk at the end of the day. Also, as the babies grow and get stronger, they will be better able to get the milk out and you won't have to do these marathon feedings.
I suggest shelving both the pump and the bottles. Pumping is just stressing you out (1/2 an oz after nursing is totally normal, by the way) and making you work harder than you need to be. If you are worried about your babies' intake, just watch their diapers. Good diaper output means good milk input. And the bottles- first of all, at only 3 weeks it's not recommended that a baby get any sort of artificial nipple at all, since it can screw up the baby's latch, and second, every time you offer a bottle you risk your babies learning that fussing means getting bottle-fed. Since it's easier to eat from a bottle than the breast, many babies learn to stop nursing, fuss, and thereby demand a bottle instead of working to nurse.
I really think you're doing an absolutely terrific job. It sounds to me like your pediatrician may have (unintentionally?) planted a seed of doubt in your mind- if she rarely sees moms of twins able to exclusively breastfeed, then maybe you can't do it either.... But you can, mama!!!! You can and you are.
Coolest thing my big girl said recently: "How can you tell the world is moving when you are standing on it?"
Coolest thing my little girl sang recently: "I love dat one-two pupples!"