My exclusively breastfed daughter only had a bowel movement every week and a half, I could almost mark it on my calendar in advance she was so regular. Its completly normal for a breastfed baby to have a long stretch between BMs. The body metabolizes it perfectly so there is no waste to be dispelled, unlike with formula. Enjoy it while it lasts! Once you start anything else (formula, solids, etc.) you will be changing a lot more soiled diapers (and who really wants that?).
I just read some of the other responses and wanted to add that in the first two months after birth, an exclusively breastfed baby will have frequent bowel movements due to the laxative nature of colostrum. Also initially, wet and soiled diapers are monitored to assure that there is adequate nutrition intake. Following this period, it is quite typical for a breastfed baby to go as long as you have described between BMs. It does not mean your breastmilk is too concentrated or that your baby is not getting enough. And having BMs less frequently does not mean the baby is irregular or constipated, only if the stool is hard and difficult to pass. My mother had a lot of misinformation to share with me. With formula feeding the norm for so many years, many people just don't know what to expect, and so they offer well-meaning advice that is not always accurate and can be alarmingly. Another good resource besides this site is kellymom.com.