I think there is a typo error in mentioning the dates. The ideal way in the present scenario to exclude/confirm pregnancy
is to go for a blood test
to assess serum beta-hCG along with a trans-vaginal sonogram and a complete evaluation by a specialist for proper management. It could be a hormonal
disturbance which is seen with sudden weight changes, stress, infections and certain medications apart from alterations in the hormonal milieu of the body due to hyperprolactinemic states, polycystic ovaries
and so on. Hope you find this information helpful. Good luck.