OMG! I am sooooo in the same boat with you! Whoever told me that aweful little lie about exclusively BFing and not having a period must have thought it a cruel joke!
I exclusively feed all my children for their first year and....
With my first daughter, I "post-partum" bled for like 10 weeks. The docs attributed it to me getting my period immediately following the birth. It was not fun. I pretty much cycled immediately after that and it was normal to "short" (i.e. less than 28 days). Ugh!
With my son (the second child), I only post-partum bled for like a week. I felt so much stronger after him. I attributed that to the doctor doing a really good clean-out job as she was having trouble stopping the blood (so I have been told). About 3 to 4 months later, I seemed to be having a cycle.
With my last child (also a girl), I went the longest with no period - almost 6 months! I was so nervous waiting for it, like every day that I did not even get to enjoy the time "off" (not preggers and not cycling!). Once I did start, my cycle was so long - almost 45 days. Now almost a year and half later, I am finally evening out to my old "normal" 28 day cycle.
I have found that each woman's experience is unique and that we just need to be gentle with ourselves, our bodies and others. I wish we all could stop spreading such generalizations and starting sharing all the uniquiness instead. I mean, really, what is the difference if this situation is "common" or not. It happens and it really is okay. You are okay. You are "normal".
(Sorry for the ending rant - the stats are interesting though....)
~C.