I have a son who had to be admitted to hospital frequently WITH asthma meds in place: before we got the diagnosis, he nearly died. Please, please, stop and think how you would feel if you were unable to take a deep breath. Not once, because your kid is sitting on your chest. Not twice, because your kid didn't get off your chest when you asked them to- but for HOURS.
I know it's a huge shift in mindset, to acknowledge that the 20th and 21st century created a medical condition that isn't responding at all to natural therapies: but the evidence just isn't there to suggest that asthma does. Some things can help- eating a diet super-rich in fruit and vegetables makes a difference, and a diet rich in magnesium helps. The salicylates stuff is interesting, yes. A back massage helps my son relax after an attack, and essential oils can play a big part of this. But his reliever inhaler, his preventer, his long-lasting reliever and the singulair are the bread and butter of his treatment and looking at the difference in him, he's like a different child.
I know this isn't what you want to hear. I know that you really want someone to tell you that a chiropractic adjustment will help, that it's not that big a deal- because that's what I wanted, more desperately than anything. I can't tell you that, though
Saying that, I'd be concerned about a doctor who prescribed a 3 week course of oral steroids. 3 days, yes, no problem. 3 weeks?