NAUSEA NAUSEA NAUSEA

Been having episodes of nausea that has been getting increasingly worse for the past 2 yrs. Used to be just early mornings & afternoons like clockwork & only for 15 mins. Now it is every day, any time of the day & for 30 mins or longer. Doesn't matter what I eat, if I have eaten or where I am in my cycle. Obviously not pregnancy. I never actually vomit, but it is as painful & uncomfortable as right before you get that rush of fluid in your mouth ...like that level of intensity. What are some things that could be causing this???