How to get prescribed a cpap?

I would go through the primary care doc. Go in for an appointment, explain your symptoms (fatigue, drowsiness, etc.), the results of your recent sleep study, and update him on your meds. I would think that he will again order a sleep study (since the most recent doesn't seem to hold much value) and hopefully they catch the problem the second time around. The CPAP may or may not be answer to your problems, though.