K.Z.
Newborns should be nursing about every 2 hours from the start of one feed to the start of the next, s if they nurse for 25-45 minutes, then you have about 1.25-1.5 hours until the next feed. They are establishing your milk supply, that is one of the biological reasons for frequent nursing, also, since their digestive systems are immature, they need small amounts frequently. Their feedings sound normal.
Your body is adjusting to the twins and you may be overproducing, not that they are under-eating. You do not need to supplement with formula. Many women do not get much out with the pump because most women's bodies respond better to the baby than the pump. The highest point of milk production is during nursing so your breasts do not need to "fill up" before you feed and do not need to be "empty" after you feed. You are lucky that your body is responding to the pump, because you can pump and maybe have someone else feed them so you can get some rest. However, if you are overproducing, pumping will only keep that production rate too high, so if you think you may be overproducing, don't pump until your breasts are empty, just pump enough for the next feed or to relieve engorgement.
Also, co-sleeping can help. If you aren't comfortable having your babies in bed with you, there are products like the Arm's Reach Co-sleeper that attach to your bed or you can just put them in a crib, pack-n-play or bassinet in your room so that you can nurse with as little disruption as possible. With two this is probably a lot more difficult, but you may be able to nurse on your baby and put one on each side. I'm sure the nursing multiples websites that Kelly Mom links to have different strategies.
http://breastfeedingtwins.tripod.com/MainPages/frameb.html
Link to other breastfeeding of multiple sites:
http://www.kellymom.com/bf/start/basics/bf-links-multiple...
I suggest you do the following:
1. Talk to a Lactation Consultant. They usually have scales where you can go in and weigh your babies frequently to make sure they are gaining weight. This will reassure you and the LC should be able to give you strategies to help you cope or correct any problems.
2. Stop supplementing with formula. You have plenty of pumped milk, so just use pumped milk. Drinking from a bottle is easier so sometimes babies get lazy and don't want to nurse from the breast if you give bottles to soon. The recommended age is 4-6 weeks to start the bottle or pacifier (even with pumped milk, but since you have twins it may be too much and you may need the break that the bottle provides, just try to use breastmilk instead of formula). the good news about the extra work babies do to drink from the breast is that it works their jaws and helps prevent fluid buildup in the ears and therefore, ear infections.
3. Turn your ear towards their mouths and try to listen for swallowing sounds. It can be hard to hear a newborn's swallow, but try, because if you do hear it, it will be reassuring for you. If you don't hear it, don't worry, it is hard to hear with really young ones.
4. Get an Arm's Reach Co-sleeper or move the babies cribs or pack n play into your room. You will get more sleep and feel less crazy.
5. Get online and check out the sites and connect with other moms of multiples who have nursed successfully to find out their strategies and experiences.
Exclusively nursing multiples or nursing/feeding without formula is possible and the other moms of multiples and the LC can help. You may decide later at some point, things become too much and you want to supplement with formula, but biologically, it most likely isn't necessary for you to supplement with formula.
Also, keep in mind, the first few weeks are hard, the first few months are easier but still hard, but once everything gets regulated and worked out, things are so much easier. After the 3 month mark things get very easy because most of your problems have worked out, your supply has regulated to your babies' needs and they aren't nursing quite as often. So hang in there and try to get some professional help. If you don't have an LC in your area try to find a local La Leche League chapter. You can do it!
Here are some other links for a breastfeeding boost:
http://www.askdrsears.com/html/2/T026200.asp
http://www.drjacknewman.com/
http://www.breastfeeding123.com
http://breastfeeding.blog.motherwear.com
http://www.llli.org//
Good luck!