Must I fast three days as an expiation for an oath (kaffarat yamin) for taking a French medicine, knowing that I swore not to put anything into my mouth from the products of the enemies of Allah and that I am still boycotting?

If you swore to boycott the products of the enemies of Allah, then you drank medicine manufactured by the aforementioned country, you have broken your oath, and atonement for your oath is incumbent upon you. The atonement for an oath is to feed ten poor persons, or clothe them, or free a slave. If you are unable to do that, then fast for three days. This ruling applies if there was no specific intention in the oath. However, if by "enemies of Allah" you intended Israel and Denmark, then you have not broken your oath by using products from other countries.