As person who has borderline sleep apnea I have noticed that the sleep apnea is less noticeable when I've lost some weight. At this time I personally would be doing myself a favor by losing 20-30 pounds. My question to you is 'Are you overweight?' If so, you may want to look into some diet changes so you can lose the weight. I personally found the reality show 'The Biggest Loser' very informative, however I've struggled with getting motivated to lose the weight. I personalloy do not believe asthma causes sleep apnea. Good luck in you search for better health.
One thought is that the swelling caused by asthma could be swelling up your breathing at night.