Yes, yes and YES! We had the same routine with my daughter...she pooped once a week, if that. My pediatrician was not all that concerned either. She wanted us to give her brown sugar or karo syrup in her bottles to loosen her up but that did nothing. If only I knew then what I know now.
It's perfectly OK for a baby who is exclusively breastfed to poop far less (up to 14 days between BMs) than formula-fed babies. Breastmilk is very efficiently made - it contains no fillers, so your baby is really getting all she needs, and there just isn't very much waste. As long as your baby is gaining weight and growing well, there isn't much you can do. Once she starts solids (and don't feel rushed to start before 6 months) she will poop more regularly - that's exactly what happened with my daughter.
Constipation is NOT an issue of how often, it's an issue of consistency. If your daughter is straining, crying when she does poop, and the poop is small, hard and formed, then talk to your doctor about adding fruits, juices, suppositories, etc. If she's having normal stools, she's really ok.
If I had known all this 4 years ago, I would have been able to enjoy my daughter - and far fewer poopy diapers - more. My son is just the opposite, up to 5 poops a day, and they are both perfectly happy, healthy children.
Ultimately, call your doctor if you have any concerns, but I think you're fine!