Why am I not getting my period

Ok so I'm 5 mos postpartum and I have only bleed once. 
I got what I want to say was my period Aug 4th it lasted my normal length of 5 days but it was like a brownish red color. Then it was supposed to come back on in September didn't get one took a test it came back negative. And now October was supposed to get one and didn't I don't know what is going on. I do breastfeed could that be it please help.