I've had sever nausea and stomach/intestine pain for about 18 hours. lots of dry heaving no vomit, abut of diareah. sever back, chest pain, headache?

Suggestions: Your symptoms indicate a possible viral GI infection. If there is a high fever, blood or mucus or, respiratory difficulty, I would suggest seeing the ED and following up with your PCP on Monday. If you are not improving in the next few hours, you have the option of going to an urgent care center. If not, staying well hydrated, resting and avoiding dairy products will help your recovery.