How can i tell the difference between a interstitial cystitis flare and a bladder infection?

IC vs UTI: Many times you can't tell the difference; and often a "flare" if ic can be precipitated by a uti. Check the appearance of your urine through a clear glass - if "cloudy" or foul-smelling it's likely to be a uti, but it could also be a UTI (early) even if grossly clear and without a odor. The best test would be a urinalysis and follow up with your urologist.