If you have no milk you should go see your doctor.
A piece of retained placenta can cause you to not have milk, as well as lead to infection. It could mean you need a D&C, or that after a few weeks of pumping, your body will reabsorb the piece of placenta if it's small enough, and then your supply will increase.
You can also ask that they run a full thyroid blood test, as thyroid may swing from hyper to hypo and back again after delivery which can impact supply. If you get meds to stabilize your thyroid you may be able to breastfeed normally.
You can ask for hormone testing. If you have too low of prolactin levels, you will not have a good milk supply. You can take domperidone to raise the level.
If you are not having a good oxytocin release, which oxytocin causes let down, you can get meds for that as well.
You may also need a different pump, a better/longer pumping schedule. most women have to learn to let down for the pump, and will struggle to pump at first. consistently pumping every 2 hours around the clock for 15-20 minutes after the milk stops flowing will stimulate a higher milk supply. while establishing your milk supply, not pumping often enough may signal to your body to dry up your milk.
Remember when born baby's stomach is the size of a marble, a teaspoon of colostrum is all they need. After your milk comes in, they still should never need much more than 2.5-3 oz every 2.5-3 hours, as breastmilk changes in composition so a breastfed baby rarely will eat more than 3-4 oz, even when similar aged formula fed babies will eat 5-8 oz bottles, cause formula is stuck at the same amount of nutrition and calories per ounce, while breastmilk can vary from 15-40 or more calories per ounce. so amount is not all that with breastmilk.
know that I could never pump more than enough to cover the bottom of a bottle, well one time I did pump 4 oz, but that was a fluke. I nursed my babies for 22 and 29 months. what you pump is never an indicator of what baby can get when nursing. A baby uses manual manipulation of the milk ducts under the areola to get milk in addition to suction. that is why baby's latch is so important so they latch on deeply enough to get to the areola. A pump only uses suction. and not all pumps are created equal, some women need a hospital grade pump, some a double electric, and some women let down and pump better with a small handheld pump like an avent isis. and some pumps suck!
If you want help with your breastfeeding come to the breastfeeding board, and go see an IBCLC lactation consultant for more help. if baby will latch on they can do a pre and post nursing session weigh in on a very accurate scale, that plus info on how much and how often you pump can help them to figure out what is going on.