I am new to this forum so I hope it is ok for me to barge in asking a few long questions about my flute playing

I used to play the flute for 2 years back when I was younger (15 years ago - am now 29 years old). I've been playing it again for the past six months (in the process I've also purchased a new advanced flute since my old one was really old and not functioning well).
I have a few questions that really bother me ...
1) When I play the first 15 minutes everything is cool and the sound I produce is for the most part pleasant (one can always improve though).
It is afterwards when the flute dampens from my own saliva that I start struggling to produce a nice sound out of the higher part of the 2nd octave. It is usually extra horrible when these notes are slurred from or to. By and large C3 & C#3 are the most spiteful


Needless to say the situation is exacerbated as I further struggle to produce these notes making a mess out of the other notes as well... Strangely enough, cleaning the flute at this stage is hardly helpful.
2) When I get 3 (or more) "all 1/16 notes" measures I have trouble breathing and choke towards the end, especially if the measures contain high notes (usually if the highest note is C3 I'd be able to finish 3 measures but it takes so much air from me that I get exhausted). I should also point out that I have some form of asthma or bronchitis (which my playing the flute actually helps keep at bay) that probably hurts my chances of completing these measures.
Is there anything that can be done to alleviate breathing through such throngs of 1/16 notes measures?
3) Slurring from E2 to D2 and from E2 to F#2... How quick are you to resort to trill fingerings when fast slurring is required? should I insist on getting my pinky and ring fingers agile enough when I play 1/16 notes and only resort to trills tackling 1/32 notes?
Thanks for bearing with me through this long post
