Sleep Apnea and BiPap

I've been reading a lot of post and really feel like I don't know near enough about my diagnosis or my machine. I was diagnosed in febuary of 2013 after a sleep study and was given a bipap machine, shortly after I started using a wedge pillow to sleep due to a shoulder injury after a car accident and started having trouble with using my machine. I had another sleep study done in April and the settings were changed on my machine, for months I was able to use it without any trouble at all but lately I've been waking up at night with sever dry mouth to the point it hurts to even swallow and I'm not really sure what the problem is. I've read a lot of posts saying it is caused by mouth breathing but it seems odd to me that it would just start happening, and it's not every night. I'm not sure where to go from here so any advice would be appreciated.

Hi - mouth breathing very commonly starts at any time after being on Cpap even for years. It can happen after gaining or losing weight, and/or after changes to Cpap pressure, and/or after having a respiratory infection, and sometimes just because we get older, our anatomy changes very slightly, or we change pillows... but we then have to look at full face masks (there are lots to choose from now), or taping. Chin straps can help, but don't always keep air from escaping through lips even if jaws are held more or less closed. I'd look at Cpap.com to see the different types of FF masks available or go to your DME and see if they'll let you try some on, but lying down (your face changes when you do that of course). I'd also look at Pap Pillow.com (they have cutouts for the mask so you can sleep on your side).