Funnily enough just listening to Woman's Hour on Radio 4 and there are clinical trials going on re one of the ingredients in the vaccine and heavy periods.
The research was going on before Covid but hard to find funding (obviously - it's only periods so who cares
) but now it is going ahead.
The dose used in an emergency eg a covid vaccine is far far higher than would be used for ongoing treatment of heavy menstrual bleeding.
So yes the covid vaccine probably is the cause of your menstrual irregularities.
It's a shame women weren't made more aware of this potential side effect so realised it was normal.