I used to have asthma when I was like 5 years old. I'm 19 now, a...

I used to have asthma when I was like 5 years old. I'm 19 now, and for some strange reason it started coming back. The doc prescribed dexpak and singulair about a week ago. My lungs are feeling great, but as far as the negative side effects go, I haven't really noticed a change in much of anything, really... I am on my 6th day. I skipped one. I work out every day, and since I started I have gained muscle mass. HOW CAN THIS BE? Does the saying, "steroids are steroids" apply here? Or are the testosterone boosters I'm taking along with this drug probably the cause. I've also read that Dexpak causes protein catabolism. Is this true? Someone help me out here!