Late period

Esther

This is probably tmi, but my cycles used to be very strange (40-42 days), after I got married they turned into 30-36 days, and stayed in the average of 34 for a couple of months. This time I’m on my 40th day, had some backaches (like I typically do before my period) about a week ago, but still no period. I took a test on 39th day, and it came out negative. Any ideas what this might mean? (I’m not on pills or any other medications). Is this okay?