It's your stomach acid, and like the above said it's from your tummy being empty.it happened to me every single day until 17w. Try to eat right when you wake up and ask your dr about nausea medicine. Hope you feel better soon
I had the same problem it's from having no food in your stomach try eating something bland as soon as you wake up like toast or something. But if your anything like me you will just end up throwing that up too lol I had to get meds for my sickness. Good luck