Antibiotics are prescribed for bacterial problems: whether it's the bacterial problems or the antibiotic that cause problems with glucose level is immaterial. It's a bit like asking the fire brigade in do do the dusting after a kitchen fire ;-) You just do what you can to pick up the pieces afterwards.
The important things about antibiotics are that (a) they don't work on viruses, (b) just because your best friend had the same symptoms and was prescribed antibiotics doesn't mean they're right for you, and (c) TAKE EVERY LAST **** PILL THAT WAS PRESCRIBED!!! (sorry for shouting, but multi-drug-resistance IS becoming a problem in the UK)
Infections that need antibiotic treatment can casue serious damage to you a lot faster than diabetes can, so prioritise emergency treatment of bacterial infections over ongoing diabetic treatment. Yes, A sudden influx of antibiotic can kill of an awful lot of of benign, helpful bacteria in the gut: get thee to thy delicatessen and buy (and eat - it's surprising how many people think that because it's sitting in the fridge, it's somehow magically protecting everybody...) live natural yogurt. Yep, the same stuff that acts as a substitute for single cream (last night's chicken korma turned out beautifully, by the way - no-one figured out I'd replaced the cream with yogurt!)
To the best of my knowledge (and I'm not a doctor, just a frequent and unwilling consumer of a major portion (or so it seems) of the Pharmacopeia), amoxycillin is a moderately powerful, broad spectrum antibiotic. More Fairy Power Spray than Cillit Bang.
My experience with HIV has taught me that if you have multiple things happening at once, you have to prioritise: X can hurt me most so we'll knock that out first and worry about the mess later; then we can start hitting Y while we're clearing up the mess from X and so on.
Hope this makes sense/helps...
Steve