Anyone else BFing? And not know their cycle length?

I'm ttc and BFing. I've had one period but I'm not sure how long my cycle is yet since I've only had one period in 18 months PP. 28 days? 30 days? 31 days? Because I haven't had another period since my last one which was 30 days ago. Took a test and it was negative! Anyone else find it hard to track your fertility when nursing? I kind of wish there were more options or question on this for nursing women.