Breastfeeding so why have I got my period

Today B is 11 weeks old she is exclusively breastfed but today my period has returned.  I thought that until you gave up breastfeeding this didn't happen but on researching via the ever knowing google seemingly it can.

Apparently when you are breastfeeding you can ovulate as early as nine weeks after you've given birth with your period returning two weeks later ie 11 weeks as in my case.  According to babycentre you are more likely to get your periods back early if your baby sleeps for periods over four hours during the day or more than six hours at a time at night if you supplement their diet with formula or solid food or if baby has a dummy.  B regularly sleeps through the night from about 11pm till 6-7am so unfortunately this looks like the reason my period has kicked in, as much as I hate all that side of being a woman I love my sleep more and if that's the price I have to pay for a baby who let's me have a good nights sleep then so be it.