Is an infection in my nose related to a previous diagnosis of and treatment for acute cystitis? could both be caused by yeast overgrowth?

Very unlikely: I have never seen a yeast infection in the nose but have seen sinusitis caused by a different sort of fungus, aspergillus. You can be relatively sure it has nothing to do with treatment of your bladder infection. You should have a culture done to see what is causing the nasal infection. There is a slight risk of lymphatic spread of infection from your nose into your brain.