Also, I can't choose a name. Its between Amy, Sydney and Kairi. Anyone willing to give their two cents?
(Note that my suggestions are based on personal preference, so feel free to disagree entirely.)
I would skip Sydney. I tend to feel like androgynous names, or closely androgynous ones, make the question of "is that a boy or girl?" more prominent at a point in life when you don't really want that. ...Unless you
do want that.
Of the two remaining- Amy is common, ordinary, uneventful, perfect to blend in. It's safely female, so no issues there. Kairi is a little more uncommon, and it's in that "constantly respelling" class of names. Say it out loud and you can get a bunch of viable spellings (Kari, Carrie, etc). Worth keeping in mind. (My therapist thinks I'm Zo; I keep having to tell him, it's Zoe, that's what it's supposed to be, the other spellings are the weird ones.)
Also worth thinking about- what's your nationality and heritage? Amy has a pretty safe Anglo-Saxon feel. Kairi does as well, but it has a different feel to it that I can't exactly pin down. I'd suggest looking up etymologies on any names you plan to use; just focus on national origin, don't worry about meaning. Nobody gives a crap if your name means "tranquility".
But your name should loosely fit both your background and presentation; you don't need an Asian name if you're Japanese-American but raised strongly on the American half. But if you're American and white don't even try Asian.
Getting into overanalyzing territory, phonetics. Thinking about myself and my coworkers, we all have three- or four-syllable names, and the vowel sounds are generally distinct, and they all sound normal. I currently have ah-uh/eh-oh; my female name has oh-ee/ah-uh. (I even managed to keep it up for my middle name, to have oh-ee/aye-ee/ah-uh.) A little repetition on unstressed syllables works, but too much stressed repetition feels artificial or sing-song-y. Amy goes a-ee, Kairi goes eh-ee (unless you pronounce it kaye-ree). Mind your last name more than your middle name in deciding the pattern.
If you care enough for you family that you plan to keep your current last name, you can win brownie points with your parents by finding out what female name they were considering for you and using that, either as a first name or middle name. This is assuming they had one and can remember it. It can go a long way in emphasizing to them that you're still their child, just you're now their daughter.