Honestly, what you're going through sounds pretty par for the course at close to a year postpartum, cycles can stay unpredictable for quite a while, and a delayed ovulation like day 39 can just push everything back, so a late period after that isn't too surprising. From what I've generally heard, some women's cycles settle into something totally different from their pre-pregnancy normal, and it can honestly take years for things to fully stabilise, one thing I've come across is that it can take up to seven years for your cycle to fully go back to how it was before. The fact that your ovulation was unusually late this round could be the main reason your period is delayed, since if you ovulated on day 39, three weeks after that would still be within a reasonable window. That said, since it's a noticeable shift from your usual pattern and it's lingering, it's still worth popping by your gynae just to rule out anything else going on hormonally, better to have peace of mind with a proper check rather than second-guess yourself.