As a fellow asthma patient, I'll say that if I were you, I'd be asking my doctor to a referral for a specialist! A GP is great, but if your asthma is still bad even with combination therapy and you can't figure it out, you need to bring in the big guns. It could be that you have a complicating condition (GERD, for example) or something other than asthma entirely.
If you haven't been to an asthma education center yet, I'd also suggest you look into that since they can help you recognize what your triggers are and learn more about your disorder. I found my asthma education program very useful, even after 22 years of asthma. If you're starting out with managing your health entirely on your own (which I imagine is the case if you're 18), they can give you the tools and knowledge you need to do it effectively.
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