How long have you been studying?
You should use "an" before a word that starts with a vowel sound.>I'm studying to become an English teacher
And use "am I" when you are asking and "I am" when you are answering or else.>How am I doing? uwu
However that's just my empirical knowledge, I didn't have taken English classes besides basic level (primaria, secundaria y prepa jeje porque en educación superior
no es obligatoria y me ha dado huevita meter Inglés).