I think ruling out sleep apnea is something to be addressed. Secondly, being told you are feeling stress is a bit flippant. Secondly if your doctor has determined you are suffering from severe stress why hasn't he treated you for it or referred you to a psychiatrist?
Everyone has stress, but is your stress beginning to manifest into an anxiety disorder or even major depression. Depression and anxiety often go hand and hand. If your physician is not willing to discuss the sleep apnea issue with you and refer you for a sleep study (which is the only way to make a definitive diagnosis) I would seek a second opinion. Considering your problem has not been correctly diagnosed in 2 years a second opinion would still be a good idea.