I've had really strange period symptoms after both the covid infection itself and after the Astrazenica vaccine, so I think it must be something to do with the spike protein, which is common to both.
The thing that happened to me was that my period was completely normal right through the acute phase of infection (6 weeks) but when my next period started, my blood pressure fell really low and I felt very weird for several days, until it normalised. I also had much heavier bleeding than usual.
That happened one more time, but more mildly, and then my periods went back to normal.
Then separately over the following year, I just had this weird thing where my blood pressure would suddenly go really low for no reason, and I'd have to stay in bed until it came back to normal. Sometimes that takes several days and that is still happening to me 16 months later, but not connected with my period
The other funny thing that happened was that it was exactly the same after I had the astrazenica vaccine. The first period after that, my blood pressure went really low and I felt really weird again, and once again it took about a week in bed to sort it out. The bleeding was not heavier that time though.
The blood pressure thing is still ongoing.
Sometimes it goes right down from a normal reading of 120/80 to 82/52, with no apparent trigger. I'm certain that that is a side effects of having had a covid infection though, and the recurrence after the vaccine must be to do with the spike protein rather than some side effect of having had a vaccine.
I'm in the process of being referred to the long covid clinic and I have reported all the side effects of the vaccine and all the symptoms of covid on every online survey I can lay my hands on.