You might be getting air in your stomach, this could be helped by using a different mask, via nasal mask, if you are currently on a full face mask. This is a common issue, ask your MD what is best for your problem.
I can't imagine why the C-Pap machine would be causing you to have a sick stomach in the morning except that the volumn may be too high and you are getting air into your stomach. I suggest you talk to the doctor that put you on the machine and he may be able to adjust the air flow to a more tolerable pressure. Good luck.