Feeling sick all the time like my food's not sitting right?

The past week i've been feeling sick quite often, and extremely thirsty. I have been drinking a lot of water but it doesn't seem to help! My mouth is always dry and I feel really thirsty no matter what. The water seems to pass through me quickly too, like it's not getting absorbed. If I eat, the nausea sometimes gets the best of me, and I end up throwing up. The food is super dry when it comes up, like I haven't been drinking anything to help with the digesting, so my stomach rejects it. I don't know why any of this is happening. What do you think it could be? Pregnancy, diabetes. just a stomach bug?