Whoa Nelly! I need to check here more often.
You cannot feed a baby that young on breastmilk exclusively and be pregnant at the same time. The fact that you GOT pregnant while breastfeeding her exclusively is an indication that your body is not producing enough prolactin to keep nursing. You need to start giving her formula. With that said, pumping is utterly in vain and I'd advise you to stop now before you drive yourself bonkers. You are supposed to have supply issues when you are pregnant. . .Likewise, you cannot take a prescription galactagogue. Those prescriptions are generally for other medical conditions that have the side benefit of increasing production - but you are pregnant. So not only is the prescription out. . .but you cannot be focused on increasing production.
As far as a schedule goes. . .once you have her weaned to formula that will be a little easier. But the way you do it is just gradually work towards changing the time in 15 minute increments.
And congratulations on the pregnancy.
