I'm still breastfeeding my 5th child, and I got my periods back after 3 months.  There is no reason why a woman should stop breastfeeding just because she gets her periods back.  In fact, breastfeeding helps to reduce bad symptoms of a period like cramping etc.  They are also generally shorter too.

No reason to stop - most mums who breastfeed for any length of time find they return before the end of feeding - I fed DD1 for over a year after they returned and nearly a year afterwards with DD2. With me the trigger seemed to be that my baby was sleeping better/through, but everyone has different experiences. With DD2 I had no periods for about 20 months - it was great! Everyone is different and I guess you have an earlier trigger point than me - sorry/great (delete as appropriate )!