I totally agree with Susan. Time, time and more time! Don't be in a hurry at 21. And since you were msicategorized as a baby spinto it would seem the voice is substantial.
By fluty, I do mean on the lighter side of what your true sound should be. It is only deductive reasoning, considering the loss of your lower range.
Another possibility could be that there is not enough breath pressure/support for the sound you are attempting to sing (sound begins in your imagination). In such a case, the folds will tighten to produce the pressure even though the resultant sound will not be very full for lack of air. The tightening could cause a loss of both extreme high and extreme low.
Finally, the second passaggio (if that is what you are referring to) is too high. Acoustic passaggio in the upper end would occur around Eb5 to Gb5 not above that. If you feel a muscular shift around A-Bb5, it could be an early muscular shift from modal voice to a flute voice (extremely reduced vocalis activity because of too much vocalis lower in the range).
I don't know your voice, so I cannot say anything with absolute certainty. But there might even be a possibility that you are between spinto and coloratura. Perhaps a lyric when the top is full enough without pushing. All maybes.
Real answers can only be found by the teacher who is working with you. What I offer here are possibilities based on the info you give.
All the best,
TS
Be not the slave of your own past. Plunge into the sublime seas, dive deep and swim far, so you shall come back with self-respect, with new power, with an advanced experience that shall explain and overlook the old.
Ralph Waldo Emerson
TS's Blog:
http://tsvocaltech.blogspot.com