Taken Bi-pap For Apnea. Feeling Tired, Falling Asleep At Work. Oxygen Levels Normal. Feeling Out Of Breath

I have been diagnosed with apnea. I am treated with a bi-pap and use it faithfully for approx. 5 years now. Lately, however, I have been extremely tired and have fallen asleep at work and while driving. I cannot go on like this putting myself and others lives in jeopardy. I have talked with my sleep doc and he says he is "dumfounded". We did try an oxygen bleed into my machine, but my oxygen levels are fine, so after a year of that, they have taken that off. I am a shallow breather. I often feel out of breath. I am otherwise an active, healthy 69-year old female. HELP. I am not sure if I should pursue this and if so, with another physician? HELP! Need some direction as to what to do next. Thank you