Dear sister in Islam, you must investigate the matter and fast what you believe you missed of the days of fasting.And ask Allah for help and assistance. “Allah burdens not a person beyond his scope” (al-Baqarah 2:286)
Do your best and investigate the matter and be cautious with respect to yourself until you have fasted what you believe must be the amount you missed. You mus also repent to Allah.
Shaykh `Abdul-`Azeez Bin Baz
Islamic Fatawa Regarding Women – Darussalam Pgs. 145