Long cycle - what does this mean

So I got off bc in January and had regular period ( 28 days) until June when my DH and I started TTC. Ever since then they have been irregular and the past 2 months have gotten longer. This month is 40 days. So my period is late but tests say bfn. What does this mean and why is my period so late? I've used ovulation tests and they are positive so I'm pretty sure I'm ovulating. This is just very confusing.