Is dry mouth, being constantly thirsty a side effect of birth control pills or something else? maternal great grandma was insulin dependent diabetic

Not due to BCPs: Hi. No, constant thirst is not a side effect of BCPs. Diabetes is certainly a possibility, although likely not related to your great granny. Are you urinating a lot? Are you overweight? If you're not overweight, remember there's a bump in type 1 diabetes in the 30's; if you're diabetic, it could be type 1 or type 2 depending on several variables. It's easy to test for. Good luck!