I am having a similar problem. My DD is 5.5months old and while in daycare she is drinking 3 bottles with 4oz of EBM. I am LUCKY if I am able to pump out 2 bottles with 4oz daily and this is with 3 sessions each 3 hours after the previous one. She is on the smaller side and we've had concerns about her weight gain, those have finally been backburnered as she is finally moving on track again. Even using More Milk Plus I've not noticed any real difference. I have one extra pumping session in the AM, since she is going for 5 hours stretches and that's how I make my last bottle.
It's definitely frustrating... anyone have any tips?