What Causes Dryness In Mouth And Rust Coloured Tongue After Using CPAP?

I use a c pap machine and I wake up with very dry mouth and copper rust colored stuff on my tongue and teeth I think blood. I also have a pain on my mid left side spleen area and tired throughout the day. I have been to ER and had blood tests they said all looked normal and they gave me meds for heartburn and acid. Is there anything else I can do