Using CPAP after surgery

I had RNY in November. Prior to surgery I used a CPAP machine for 2 years. I used the CPAP in the hospital after surgery, but apparently had no problems with apnea in surgery or recovery (when I wasn't using the machine). I'm wondering if anyone else has experience with using their machine after surgery. How long should I use it for? And how do I know if the pressure settings need to be changed? I don't have severe apnea. Also, I've had this fear that my machine will push air into my stomach, but so far, I haven't had that problem.

I have severe sleep ap and am supposed to use a bi-pap with a setting of 16/10. Within two weeks after surgery the pressure of the air filling my stomach was so intense I called the dr, my primary, my insurance company and the oxygen supply company that provides the bi-pap. That was back in October. They all told me to keep using it as long as I could each night until I could get in for a new sleep study (was supposed to be within another 2 wks). For whatever reason I guess they never scheduled the study because I have made dozens of calls and am still waiting...finally gave up on the machine and I sure feel a difference. As much as I hate it, I think I need it still- just at a lower pressure. But that doesn't happen to everyone, as you can see from here- most people don't notice a difference in the pressure in terms of their stomachs.