thanks for query,
You have started Menopause
This is a period usually started after 40-45 years due to hormonal
imbalance where lady gets Hot flushes on face & some unexpected feeling in body the symptoms were different from individual to individual.
The monthly bleeding happens some times once in 6 moths or not happens for 3-4 months or happens every month in short it is very irregular.
As you have undergone several pregnancy
test to confirm pregnancy it is not the possibility of your missed period.
Make sure about your contraceptive
measure once your period comes because irregular periods
not give you immunity from pregnancy.