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.
^ A few more thoughts: one way to check if there's an obvious reason why your asthma is getting worse is to make a list of recent changes in your life. Then look at a list of common asthma triggers and see if anything might be connected.
Have you started any new meds?
Have you moved recently?
Have you had an illness recently (in my case, a very bad cold, followed by a few secondary infections and finally a true flu)? I know from experience that illness can cause previously-well-behaved asthma to go crazy for months and months: after 18 months, it's still not that well behaved.
Have you started university or college? How's the air quality there?
Have you started a new job? Are there triggers there?
have you taken up a new activity? Are there triggers there?
Have you acquired new pets? have you been allergy tested for sensitivity to them?
And sometimes it just happens. If you're female, it's not uncommon to have your asthma get better during puberty, and then worsen again in your late teens/early twenties, often with a move or illness as a trigger (this happened to me).
And so on. If I'd known to do to do something like that when I was first managing my own young-adulthood worsening of asthma, I would have had a much faster time of getting mine under control.
Finally, I have to emphasize: If you're not satisfied with your control, bug your doctor! Keep bugging them until they listen or it becomes obvious that they're not going to listen (in which case, find a new doctor). If you're not satisfied with your control, something's wrong.
Thanks for the advice, anyway i probabaly shoulld have added i'm a male, but anyway, there has not really been any change except that i stopped receiving shots I previously (years ago - about 3) had taken for about 6 months (which i believe were helping my asthma). I think I am going to take your advice and bug my doctor; no matter what I am sick of, her diagnosis is usually allergies or asthma related. P.S. sorry for replying late, i hadn't had time to check my e-mail. :)