Ah, yes, that's very likely it. if you need a bi-pap, you probably have quite severe apnea, and if it is at it's lowest setting, you are down around a 5 ish, so you will still stop breathing a lot.
AHI is Apnea/hyponea indicator. It is the average number of not breathing, or not effective breathing you have per hour. It is the primary way you can tell if the pressure setting you have is efficiently working. You are always looking to get your AHI under a value of 5, but as low as possible. Have a search online for the manual to the machine you are using, it should be pretty easy to check.
Once you have your pressure adjusted properly, you will probably need to get it adjusted every few months as you rapidly lose weight. As you go, signs that your pressure needs to be lowered are:
Mouth leaks: waking up to find air rushing out your mouth,
Waking up belching or with discomfort in your pouch from swallowing air
Sinus irritation unrelated to a cold or infection.
My pressure started way up in upper severe at 18, and is now down to 5... I should be off it soon, if I can take off a bit more weight!
Best of luck,