I have to pee constantly, but it's not a UTI - what could this be?

Diet. First. Make sure you don't have a UTI with a medical professional; certain foods/drinks in the diet or certain dietary habits can promote frequency; constipation, emotional stress and or learned behaviors can promote frequency of urination. Keep a diary of food/drink and frequency of peeing. If you are not getting up at night -watch out for caffeine & other daytime acts/thoughts/behaviors.