What is incumbent upon me, given that I swore an oath, "By Allah, I will not do such and such," and then I repeated the act, and on another occasion, I said, "I make a vow to Allah that if I do such and such, I will fast for an entire lifetime" — but I don't remember exactly what I said — and then I also repeated the act?

The first oath requires an expiation for breaking an oath (kaffarat yameen), which is feeding ten poor people or clothing them, or fasting for three days if that is not possible.

As for vowing to fast for an entire lifetime or for a specific period upon doing a certain thing (nadhr al-lajaj - a vow made in anger or obstinacy), the prevailing opinion is that the one who made the vow has the choice between fulfilling the vow or offering an expiation for breaking an oath.

If you choose to fulfill the vow but forget the amount of fasting you vowed, what is obligatory upon you is the certain amount, just like someone who forgets whether they vowed for Hajj or 'Umrah, in which case 'Umrah becomes obligatory upon them.