LO Weight Gain Concerns

appleh05

DD is 9 months old.  When she was born she weighed 9lbs 11oz putting her in the 75-90 percentile.  She has stayed at the 75% until her 9 month appt (14lbs 6oz at 4 months; 17lbs 4oz at 6 months).  At the 9 month appt she weighed 17lbs 8 oz so she only gained about 4 ounces in the past three months.  This dropped her to the 25%.  She nurses every four hours during the day.  She also eats about 24oz of baby food each day and has snacks if needed.  She seems happy and healthy--talking, standing on her own, etc.  The doctor wasn't overly concerned but suggested that I start pumping to see how much bm she is getting and to supplement with either formula or pediasure if she isn't getting 25-30oz of bm.  My problem is that since I'm a SAHM and have not pumped these past nine months, I can't seem to figure out how to get going with it.  I started trying to pump after each feeding 3 days ago and I am still not getting any more than a few drops at best.  How am I supposed to know how many ounces she is getting when my body knows when she eats and how much she eats and I can't seem to produce more than that?  I don't want to start supplementing if there is no need but I don't want her to need more than she is getting.