I would see you doctor regarding this to rule out anything serious.
If you are sexually active...have you taken a pregnancy test?
During my first pregnancy, I only had "morning sickness" at night, when I was tired and wanted to sleep. The only way I ended up getting any rest was to sleep in a recliner or with several pillows, so I was a little more upright.
you could just have a virus or it could be something more serious like an infection or food poising. go to your docter he/she may need to run some blood tests. drink more. you should drink at least two litres of water a day that is around ten to fifteen glass fulls. you could be dehydrated.
It could be GERD. Are you having any other symptoms like a burning in your throat?
The best thing to do is see your Dr to find out what's going. If it is indeed GERD there are meds and diet changes to help with this.