I have roughly the same thing, and while I never followed any actual keto diet, I do maintain a relatively low-carb diet. After not eating many carbs for a few days and losing some weight I also have to urinate quite frequently. That need goes away if spend a few days eating a lot of carbs (holidays where I overeat whatever I want, for example), so I'm not particularly worried about it. My guess is that it's a result from not having much to hold the fluid around in my body, so it goes straight to my bladder. Also a lot of caffeine and liquid consumption in general