In the UK, the Medicines and Healthcare Products Regulator Agency run a ‘yellow card’ system to assess side effects from drugs, herbal medicines or vaccinations. This is a passive surveillance system where anyone can report side-effects. This system in the UK has detected a possible link between COVID-19 vaccination and menstrual abnormalities.
This is worth investigating, however, the changes to menstrual cycle all appear to be temporary, with the cycle returning to normal shortly afterwards. Most significantly, there is no evidence of any effect on fertility.