How normal are irregular cycles pp?

For background: I'm 32 with one child. Before baby I was on some form of birth control for about 15 years, the last being Merina Coil for 10 years. I had that removed 4 months before finding out I was pregnant and had really regular cycles, always 28 days long.

After having my baby my periods started exactly 12 weeks pp. I'm now nearly 16 months pp and my cycles are all over the place. Anywhere between 20-30 days. They're also a lot heavier and more painful than I remember before pregnancy. Although the pain seems to be getting better with each period.

I've seen my doctor before and all they said was to 'keep an eye on it' and prescribed me Mefenamic Acid which I've never felt the need to take.

I have been tracking my cycles, although the app I use can't cope with the irregularity it averages my cycles at 26 days. My period is now supposedly 4 days late - which is the longest so far, usually if it's late it's like a day or 2 at most. Im sure I'm not pregnant and tested today with a negative result.

I dont think I'm worried? Just wondering if things might just work itself out over time, but advice welcome please!