Is the divorce pronounced during menstruation considered a valid divorce according to Sharia, and therefore, is my last divorce to my wife considered the third or second divorce, taking into account my wife's and my intention that it was the second divorce?

The majority of scholars hold the view that the divorce of a menstruating woman is valid despite its being an innovation (bid'ah), and that an explicit divorce (by clear wording) does not depend on the husband's intention, nor does his ignorance of the ruling prevent its occurrence. Based on this, your wife has been divorced from you three times, and she is irrevocably separated from you (baynunah kubra). She is not lawful for you until she marries another man (a marriage of desire), he consummates the marriage with her, and then he divorces her or dies, and her 'iddah (waiting period) from him ends. It is advised to present this issue to trustworthy scholars in your country.