How soon after starting a dose antibiotics can i get a yeast infection?

Hard to say: Taking antibiotics doesn't give you a yeast infection. The yeast are already there, but if you kill off enough germs in your gut or on the skin surface it allows them more access to territory/food so they may emerge as a problem. It takes at least a few days to start the process. If you take probiotics (good germ colonies) at the same time you may avoid it.