I'm exclusively pumping too, and you just have to go back to pumping every 2 hours (or less if you have the time). Also try to relax when you do it. Stress can cause your milk not to let down, which leaves it in there and then will keep you from making more milk. Watch the clock not the amount in the bottle. I started worrying about how much was coming out and checking the bottle every few moments to see how much was coming out and I went from 6oz every time to 3. Now I just sit back, and try to do something like cafe mom to take my mind off things and just pump for about 15 minutes. It will come back with in a few days and in the mean time you can supplement with formula.
There are natural supplements that can boost your supply, including oatmeal (eat it as cereal, granola, cookies, etc) or an herb called fenugreek. Even if you do have to use some formula, don't give up on giving your baby breastmilk as much as you can. It doesn't have to be all or nothing and your baby's health will still benefit from being mostly breastfed even if formula is used too.
The oatmeal as mentioned above will help also make sure you are drinking enough fruit juice and water are the best, also for some reason I seem to make more milk when I drink ice tea(decaf. The most important thing is not tho stress your self as your body will make less milk, if you have to give some formula it is OK she will still have all of the benefits of breastfeeding with even two ounces a day. You may want to check the Kellymom site for more info it is a super resource that my lactation consultant recommended.
There are plenty of ways to help increase your supply. Anyone who tells you otherwise is wrong.
Kellymom is a great resource. The #1 best way to increase your supply though would be to get baby to nurse directly rather than to pump. No pump is as effective as a baby.
I have struggled with low-supply/output for the majority of my daughter's life. I've done everything I can to keep it up and have not given formula. Even if you feel that you have to give some formula while you continue to increase your supply there is NO reason to stop providing your milk, even if it is just a little bit it will help!
Steel cut oatmeal is the best kind of oatmeal. Old fashioned is 2nd, instant is last.
Google "Housepoets Lactation Cookies" and make those...they are DELICIOUS! I usually double the recommended amout of flax seed meal and brewer's yeast. Keep in mind that the brewer's yeast gives it a rich full flavor and if you don't like it too much then don't double it. Both of those things can be found at GNC or other health food stores.
Fenugreek, alfalfa and fennel seed all help and are also at GNC.
I also drank Mother's Milk Tea or Milkmaid Tea 3x a day. Follow the directions on the box/container.
Motherlove makes a tincture called More Milk Plus that DRASTICALLY helped.
A "last resort" is Reglan (not if you have a history of depression) which you can get a prescription for from your doctor or Domperidone/Motilium which you can order online from inhousepharmacy.com. It takes about 10 days to receive the Domperidone usu