ugh. i was so relieved when you said you were going to request a C&S when you took alex in to see the vet on the monday the 27th.
once abs have been started, you've messed up getting an accurate culture.
i think it would be helpful if you reread your thread on the old board:
http://www.felinediabetes.com/phorum5/read.php?8,1950311,1950311,sv=1#msg-1950311
as well as dr. lisa's
Feline Urinary Tract Health: Cystitis, Urethral Obstruction, Urinary Tract Infection.
many of these concerns/questions are addressed and answered.
if your vet thinks alex has cystitis, what about a pain med such as Buprinex?
and yes, insulin needs can change drastically if there's an underlying condition... cystitis can be very painful, but i don't have to tell you that since you've mentioned it's a condition you have yourself.