I can't deal with my startups' lack of discipline and systems

My to do list was growing everyday. When I looked at the list I got depressed. I could never get it all done. I was never going to catch up. I know that I should prioritize things but I do not really know how to do it. It seems simple but it is very hard for me.

As a team we also have problems establishing priorities. Everything and anything is a priority. Sometimes there are daily changes in what we must do. We are constantly fighting fires.

The CEO often tells us to drop everything and do x. This only makes matters worse. Things are half done and some things just get lost.

When a customers calls asking where their order is, we simply fill that order next.

We can't carry on like this. A business can’t be run this way and it is driving me crazy.