No poopy diapers

My LO is 11 days old, at her first ped appt last week it was determined she wasn't eating enough (it was often hard to wake her up for feedings) so she put us on a strict schedule of 2 oz every 2.5 to 3 hours.  When she saw the ped on Monday, she hadn't had a poopy diaper since Friday.  She's doing well with her feedings now, she's awake more often and happily eats every 2.5 hours, but still no dirty diapers.  She had two on Thursday I think it was, so I thought her system was getting back on track, but now nothing since then.

She gets about half her feedings from pumped milk and the other half we give her Similiac for gas and fussiness.  I've got a call in to her ped but in the meantime, was wondering if anyone else went through this.  She's got plenty of wet diapers, but why no poopy?  She's still pretty fussy, I thought it was gas pains but since she's not pooping, could it be constipation?

ETA: I heard back from the doctor, she said it can take several days for things to get back on track, and as long as she is eating well and having plenty of wet diapers, it's not too big of a concern but to call back if it's going on six days or so without a BM.  She also said I could try using just the tip of a Qtip with vasoline and just stimulating her anus (boy is she going to hate me for that) and sometimes that can help.