Are you eating and drinking enough? It is important to consume enough fluids and nutrients to support milk production. Have you started to switch your baby to formula or breast milk bottle feedings? For some women pumping isn't enough... they need suckling to stimulate production.
There are supposed to be herbs you can take to encourage milk production, but I'd speak to a local La Leche League person if you can to find out what is going on with you.
I agree, you definitely need to make sure you're eating enough as well as drinking enough water. I've also heard of women who have had their supply drop when they get a cycle back, but I don't think this is the case for you. More than likely it's because you're supplementing as well. BFing is about supply and demand and if you're only pumping then you have to make sure you ONLY pump and pump frequently. The less you pump, the less your body thinks it needs to make and therefor your supply drops. If you pump every 1-2 hours your body responds to this and makes more. Do you only pump, or do you nurse in addition? If possible, nurse as frequently as you can. A baby is more effective than anything else at getting milk out and if you can drain most of the milk you will also make more.
There is a natural herb that I took during my breastfeeding that helped produce more milk…it's called Fenugreek
theres also, fennel (milk ejection stimilator) mothers milk tea, blessed thistle, steel cut oats or regular instant oat meal. Lactation cookies: http://www.drmomma.org/2010/08/major-milk-makin-lactation-cookies.html
brewers yeast, milled flax seed. Milkmaid Tea. fenugreek: 3 pills 3 times a day, you will know its working when you smell like maple syrup,
All of these help with milk production. they all have a common ingredient:"galactagogue" that helps with healthy lactation.
also pump, pump and pump and nurse nurse nurse. eventually your supply will pick back up. also stick with it, dont suppliment with formula it is one of the major things that cause low supply, you suppliment and not nurse or pump your supply will drop, just nurse straight though, your breasts are constantly making milk.
it took 2 1/2 weeks for me to get mine up from a few drips every 2 hours for 5 oz every 2 hours. but you might not take as long as i did for your supply to be back up/
Ok im done...i think lol
When you pumped and barely got anything did you feel your milk let down? I exclusivley breastfeed, but I pump sometimes in between feedings to be able to pack some away in the freezer and sometimes while pumping my milk just won't let down. If you are getting the letdown though the other ladies are right pump, pump, pump! Keep at it and you'll build your supply back up...Good luck!