I just started taking 250mg keflex antibiotics 3x a day for a week then 1 before bed as a preventive for reocurring uti for 6mo. will i get thrush?

Not necessarily: Sometimes people get thrush with antibiotic use but most often they don't. I can't tell you what your odds are of developing thrush.

Yeast: Keflex is a very good antibiotic. Yes, oral thrush can occur following Keflex. A 7 day course though makes this unlikely. Rinse your mouth 3-4 times a day with a very good cleansing mouth wash.

Here are some ...: I assumed the use of Keflex was selected on the basis of urine culture & sensitivity test, that is what usually would be done in medical practice. Otherwise, using nitrofurantoin or TMP/SMX has been more common for long-term preventive purpose. If going to develop thrush? No one can predict, but broader-spectrum antibiotic like Keflex would be more likely to develop thrush than the narrower ones..