How did you determine your I:C needed changing?
Your post leads one to believe that your insulin requirements are dropping your experiencing low BG? I would never suspect that my insulin requirements would drop because of infection or illness. My requirements also go up during the winter because my activity level drops and I need a little more fuel to stay warm. My I:C and sensitivity increases from morning to evening about 30%.
If your I:C is changing then your sensitivity (correction factor is also changing). Also shortening duration will increase correction insulin if your out of target range, increasing the time will make your bolus wizard a little less aggressive.
Are you absolutely sure your basal is correct, are you having site rejection or absorption issues. I sometimes have huge swings in absorption based on my infusion location and time.
If I was not using a CGM I would base my changes on 30 day averages and would spread my meals out to at least 6 hours apart so there was no active bolus insulin when I test and bolus for meals before making a change.