It's my first time being overseas since this testing requirement with instated late January, 2021. Just to confirm.. I'm a U.S citizen, who is fully COVID vaccinated.. I need to take a COVID test before I can fly back to the U.S?? It can just be the antigen test from any clinic, right?

If I were to test positive that means I cannot take my flight back home to the U.S?? Is that correct? I would need to stay in the country where I am (Turkey) until I am able to test negative?

This sounds a bit crazy to be honest.. especially since vaccines in the U.S have been available for many months to anybody who chooses or wants to get them. It sounds unbelievable that there is even a rule in place like this for U.S citizens still in November, 2021. I'm just trying to make sure I understand correctly.