My cycle has been a bit odd since having the kids, was always around 30-31 days pre-kids but it's getting longer and longer and I am currently at CD 36. Is it normal for period to do this - I had symptoms about a week ago, have been cranky feral pants and thought I felt some cramping last night but still no AF?

I am totally clueless and was worried I might be pg as we use withdrawal method and charting, and although we haven't had any accidents we clearly know it isn't foolproof(time to get Implanon I think) anyway I did a HPT last night which was neg so I really don't think I am pg, just unsure if it's normal for AF to fluctuate so much and be this late!!!!