Sick of feeling like crap all the time

In my ongoing saga of feeling like crap all the time (4 years now) I'm nearing the end of my rope. 18 doctors, MRI's, CAT scans, poked, prodded and enough blood drawn to fill two people later and yet no diagnosis. Too medications tried to list (with no success) but I am on a first name basis with my pharmacist if that's any indication.
I was diagnosed with mild sleep apnea a year ago and just got back from my second sleep study (this time with the cpap machine) and feeling very disappointed. I got about 3 hours of sleep. Even on the lowest setting, I was breathing too deep and could not relax. Who knows what's going on.
I just don't know what to do or where to go for help. I've got $20 grand (after insurance) into this so far so I just can't give up without an answer.  I got demoted at work because I couldn't keep up with my work so that doesn't help matters at all. I make it through the day at work but that's about it. I'm so exhausted I can't do anything else. No energy for a social life, hobbies, etc. Hell, I've even started sending my laundry out because I just don't have the energy to do it. 
I just want to be normal again- that's about it. 
Thanks for reading my vent.